Subscriber access provided by University of Newcastle, Australia
Article
Lanthanide-labelled immunochromatographic strip assay for the on-site identification of ancient silk Qiushi You, Miaomiao Liu, Yang Liu, Hailing Zheng, ZhiWen Hu, Yang Zhou, and Bing Wang ACS Sens., Just Accepted Manuscript • DOI: 10.1021/acssensors.7b00086 • Publication Date (Web): 13 Mar 2017 Downloaded from http://pubs.acs.org on March 14, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Sensors is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sensors
Lanthanide-labelled immunochromatographic strip assay for the onsite identification of ancient silk Qiushi Youa, Miaomiao Liua, Yang Liua, Hailing Zhengb, Zhiwen Huc, Yang Zhoub, Bing Wanga,* a.Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018, China. b.Key Scientific Research Base of Textile Conservation, State Administration for Cultural Heritage, China National Silk Museum, Hangzhou 310002, China. c.Institute of Textile Conservation, Zhejiang Sci-Tech University, Hangzhou 310018, China * Email:
[email protected] (B. Wang); Tel/Fax: +86-571-86843867
KEYWORDS:lanthanide-labelled immunochromatographic strip; on-site identification; ancient silk; silk fibroin; SF antibody ABSTRACT: The on-site identification of ancient silks has long been a key challenge in archaeology. Therefore, a rapid, costeffective, sensitive analytical approach is highly desirable. In this paper, a lanthanide-labelled immunochromatographic strip which is suitable for the on-site identification of ancient silks is described. Compared with the conventional colloidal gold-based immunochromatographic strip, this strip shows much higher analytical sensitivity and better quantitative discrimination. The limit of detection (LOD) of the strip for silk fibroin (SF) was calculated as 8.09 ng/mL, approximately 185 times lower than that of the colloidal gold-based immunochromatographic strip. No cross-reactions with other possible interfering antigens were observed. Moreover, the strip also shows good reproducibility, with a mean recovery of 94.15-102.55% and coefficient of variation of 5.22-17.57% in the repeated tests. Based on the advantages of portability and cost-effectiveness, as well as sensitivity, specificity and reproducibility, the lanthanide-labelled immunochromatographic strip is a promising tool for on-site detection of ancient relics in archaeological fieldwork.
Silk has been used as a natural source of textile materials for thousands of years due to its excellent performance properties such as lightness, smoothness, softness and comfortableness.1 Studying ancient silk is of important significance for understanding ancient sericulture, textile manufacture, apparel and accessories. Silk Road—which was "the Internet of the ancient world", arisen through the communication between Eastern and Western civilization, has an indelible influence on the course of whole human history. The road guided travellers and merchants through scorching deserts and snow-capped mountains, prompting the great cultural and technological developments that flowed along the route: music, religion, language, numerals, medicines and innovations such as papermaking.2 Nevertheless, the original role of Silk Road was to transport silk produced in ancient China to west Asia and Mediterranean. As a result, it is of great historical and cultural value to identify the origin, transmission and exchange of ancient silks. A large amount of ancient silks were unearthed in China, India, Russia, Central Asia，MiddleEast，Europe and other locations along the Silk Road, however, most of them were poorly preserved. This is mainly due to the nature of the silk
itself and the effect of poor burial conditions. The main component of silk is silk fibroin, which is easily deteriorated by humidity, heat, oxygen, microorganism, and so on.3 It is not difficult to imagine that silks were degraded into peptides or amino acids after buried in the ground for thousands of years. In addition, the earlier the silks existed, the more difficultly for the physical evidence to be found. Like silk itself, the origin and dissemination of silk are riddled with unanswered questions.4 Therefore, it is necessary to explore ancient textiles information from traces, residues and soils by the use of specific and workable analytical techniques. A variety of methods, including microscopy (optical microscopy5 and scanning electronic microscopy6), spectroscopy (Fourier transform infrared spectroscopy,7 time-of-flight secondary ion mass spectroscopy,8 surface-enhanced Raman spectroscopy9) and chromatography (high performance liquid chromatography5), have been well developed and applied to the detection of ancient silk. However, these methods are often used to infer the entire molecular structure by measuring the local information regarding the molecule. Thus, these methods would have relatively low reliability when the sample has
ACS Paragon Plus Environment
ACS Sensors
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
been contaminated by other proteins, such as human serum albumin (HSA). Additionally, incomplete and complex component samples, such as ancient silk, increase the difficulty of detection and discrimination. These methods also usually use large-scale, professional and expensive equipments, which makes them unsuitable for on-site identification in archaeological fieldwork. Consequently, a method with good specificity, high sensitivity and manoeuvrability is highly desirable. Immunological techniques, i.e. enzyme-linked immunosorbent assay (ELISA), immuno-fluorescence microscopy (IFM), immunoprecipitation (IP), immunochromatography, etc., have the potential to become a powerful diagnostic tool and have gathered increasing interest in the field of archaeology.10 Compared with the conventional methods, immunoassays have several advantages, including high sensitivity, micro-destructivity, low cost, and the ease of distinguishing different types of binder materials as well as materials from different biological sources.11 In recent years, immunochromatography, which was developed based on enzyme-linked immunosorbent assay (ELISA) and chromatography, has become a well-established and acknowledged testing technology.12 Particularly, this method is portable, user-friendly, point-ofcare and cost-effective, which makes it perfectly suitable for the on-site identification of ancient silk. Besides, the detection tool “strip” used in immunochromatography has been commonly applied in other detection methods, such as electrochemistry13 and chemiluminescence,14 reflecting its practicability and applicability. The most widely used type of immunochromatography is colloidal gold immunochromatography, which has been employed for the rapid identification of viruses,15 residue,16 antibiotics,17 disease-related proteins,18 heavy metal ions19 and silk.20 However, low analytical sensitivity and relatively poor quantitative discrimination limit its further application in ancient silk detection. Therefore, fluoroimmunoassay, particularly lanthanide-labelled immunofluorescence chromatography, has attracted considerable attention.21 The lanthanide chelates used as fluorescent labels in lanthanide-labelled immunofluorescence have a longer fluorescence lifetime than do common fluorescents.21-22 Thus, much higher sensitivity and accuracy can be achieved by appropriately extending the detection time to eliminate background fluorescence interference. Moreover, the fluorescence intensity can be determined using a portable fluorospectrophotometer for a quantitative analysis, instead of just giving a qualitative yes/no answer. In our previous work, immunoassays including ELISA, IFM and gold-based immunochromatographic strip assay were first proposed and successfully used for the detection of ancient proteinous fibres and fabrics.20, 23 Based on advantages and developments of such immunoassays, herein we describe a lanthanide-labelled immunochromatographic strip for the detection of ancient silk. The sensitivity and quantitative analysis ability of the strip have been greatly improved, indicating that the lanthanide-labelled immunochromatographic strip has
Page 2 of 10
the potential to become a powerful analytical tool for the onsite detection of silk traces in archaeological fieldwork. Experimental Reagents Goat anti-rabbit IgG alkaline phosphatase (AP)conjugated antibody (500 µg at 2 mg/mL), saline, Freund’s complete adjuvant and Freund’s incomplete adjuvant, 1-ethyl3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and Tris-HCl were supplied by Hangzhou Hua'an Biotechnology Co., Ltd. Europium chelate-loaded fluorescent microspheres (particle diameter: 110 nm, excitation wavelength: 365 nm, emission wavelength: 610 nm) were supplied by Shanghai Xibao Biotechnology Co., Ltd. Sericin and keratin were purchased from Shanxi Senlang Biotechnology Co., Ltd. Bovine serum albumin (BSA), human serum albumin (HSA), ovalbumin and collagen I were purchased from Sigma-Aldrich. Natural silks were obtained from Zhejiang Misai Silk Co., Ltd. Hydrogen peroxide, sodium hydroxide, sodium carbonate, calcium chloride, sodium chloride, potassium chloride, disodium hydrogen phosphate and monopotassium phosphate were supplied by Tianjin Gaojing Fine Chemical Co., Ltd. Phosphate-buffered saline (PBS) solution at pH 7.4 was used as the diluents for antigens. All other reagents were of analytical grade and used as received. The water used in all experiments was purified by a TPM Ulrapure water system. Archaeological samples Three precious archaeological fabric samples were chosen for immune detection. The original condition of the samples is presented in Fig1. (a). Sample A was excavated from Kazakhstan. Sample B was unearthed from a Chu period tomb (approximately 2300 years old), Anji County, Zhejiang Province, China. Sample C was unearthed from a Song period tomb (approximately 760 years old), Ningbo City, Zhejiang Province, China. The unearthed fabrics suffered from varying degrees of erosion and contamination, which increased the difficulty of identification. Extraction of antigens Cotton and hemp were extracted with the same method as reported previously.23b Silk fibroin was extracted as follows. Briefly, silk was boiled twice in 0.5% (w/w) Na2CO3 solution at a bath ratio of 1:100 for 0.5 h. Then, the insoluble silk fibroin was washed 3 times with water and dried at 60°C overnight. Next, the shredded silk fibroin was added in the CaCl2 solution at a bath ratio of 1:25 and boiled for 1.5 h. The solution was filtered to remove insoluble substances, and the obtained silk fibroin solution was dialyzed using a dialysis membrane with a molecular weight cut-off of 10000 for 3 days to remove calcium and chloride ions. Finally, silk fibroin solution was lyophilized.
ACS Paragon Plus Environment
Page 3 of 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sensors
Preparation of lanthanide-labelled anti-SF primary antibody Primary antibody specifically recognizing silk fibroin was prepared as follows. First, 500 µg of complete antigen (silk fibroin) was diluted in saline and mixed with an equal volume of Freund’s complete adjuvant. Then, antibiotic solution was added to the mixture to form an emulsion. Ear blood samples of the New Zealand white rabbits (14-16 weeks old) were drawn as controls before immunization. For the primary immunization, rabbits were injected subcutaneously with 100 µL of immunogen emulsions at multiple sites. Then, Freund’s complete adjuvant was replaced by Freund’s incomplete adjuvant to boost the immunization at 2, 4 and 6 weeks after the primary immunization. Ten days after the third and fourth booster immunizations, the serum titre of the blood sample was measured by indirect ELISA. Sera were collected when the titre reached the required value. The resulting anti-SF antibody was further purified using a Protein A column and stored (3.15 mg/mL) at -20 °C for use.23 EDC mediated method was used to couple the purified anti-SF primary antibody with europium chelate-loaded fluorescent microspheres. Briefly, 0.15 µg fluorescent nanoparticles, fresh-prepared 2.7 µL of 5 mg/mL EDC solution and 10 µL of anti-SF primary antibody at a concentration of 0.5 mg/mL were added to 3 mL of 20 mM PBS (pH 7.4). The mixture was incubated at room temperature for 2 h with gentle end-to-end shaking. The resulting nanoparticles were washed in 10 mM PBS and then resuspended in the quenching solution (40 mMTris-HCl with 0.05% (w/v) BSA) for 60 min to block free carboxylates. Protein-coated nanoparticles were purified by alternately centrifuging and resuspending in phosphate buffer (10 mM, pH 7.4) with 1% BSA and stored at 4 °C until use. All animal experiments were carried out in accordance with the national standard “Laboratory Animal-Requirements of Environment and Housing Facilities” (GB 14925-2001) and the guidelines issued by the Ethical Committee of Zhejiang Sci-Tec University. Preparation of lanthanide-labelled immunochromatographic strip The immunochromatographic strip consists of five components: a PVC base, a sample pad, a fluorescent conjugate pad, an absorbent pad and a nitrocellulose membrane. Lanthanide-labelled anti-SF antibody was sprayed onto a glass fibre membrane at the speed of 1 µL/cm using a spraying device and then dried at 37 °C. Silk fibroin (4.8 mg/mL) and goat anti-rabbit IgG (1.5 mg/mL) were sprayed onto a nitrocellulose membrane at 1 µL/cm at the test line and the control line, respectively, and dried at 37 °C. All these components were assembled on the PVC base as shown in Fig. 1b. Finally, the well-assembled strip was cut to a 4 mm width and placed in a plastic card.
Optimization of experimental parameters Silk fibroin (positive control) was used to optimize the experimental parameters of lanthanide-labelled immunochromatographic strip assay. First, silk fibroin was dissolved in PBS (pH 7.4) and diluted to a concentration of 40 ng/mL. Each 100 uL of sample solution was then added to the sample well of the strip and left to sit for various time. Finally, the fluorescent intensity of the test line of strip was read by a fluorospectrophotometer (JY1501FS, Shanghai Jie'yi Biotechnology Co., Ltd.). Samples containing 120 ng/mL of silk fibroin were assayed using the lanthanide-labelled immunochromatographic strip, to further evaluate the optimal test temperature. In addition, silk fibroin solutions of 100 ng/mL were prepared using PBS with different pH value and ionic strength to obtain optimal buffer system. Determination of LOD, specificity and reproducibility A total of twenty blank samples (0 ng/mL of silk fibroin in PBS, pH 7.4) were tested by the strip to determine the LOD, which represents the minimum concentration of silk fibroin that can be detected. The LOD was defined as the mean measured concentrations of all blank samples plus three standard deviations between them (mean+3S.D.). Eight possible interfering antigens (sericin, cotton extract, hemp extract, keratin, ovalbumin, collagen I, HSA and silk fibroin) were dissolved in PBS (pH 7.4) at a concentration of 100 ng/mL and detected using the strip to evaluate the specificity. Silk fibroin with gradient concentrations of 40 to120 ng/mL was selected to evaluate the reproducibility of the strip. Each entry was repeated 10 times to determine the coefficient of variation (CV) and recovery. The coefficient of variation and recovery were calculated according to the following formula, respectively. CV=T/CS.D./ T/Cmean×100% *
Recovery=C / C×100%
(1) (2)
T/CS.D. and T/Cmean denote the standard deviation and mean value of the T/C ratio, respectively. C* represents the concentration of silk fibroin corresponding to T/Cmean, obtained from standard curves. C indicates the given concentration of silk fibroin. Pre-treatment of archaeological samples The pretreatment of archaeological samples depends on the preserved condition. For most of the unearthed ancient samples, because they have suffered a certain degree of degradation and become partially soluble in aqueous solution, the extraction procedure can be simplified. Two milligrams of sample was ground into powder and dissolved in 2 mL of PBS (pH 7.4). After incubating for 1 h (without heating), the resulting supernatant was collected, diluted and assayed by lanthanide-labelled immunochromatographic strip. Five parallels
ACS Paragon Plus Environment
ACS Sensors
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
were used for each sample and control, and run simultaneously. All of the values are expressed as mean ± standard deviation. Results and discussion The principle of the immunochromatographic strip This fluorescence strip is based on indirect competitive immunoassay to detect silk under UV irradiation at a wavelength of 365 nm. As shown in Fig1. (b), the fluorescent conjugate pad is sprayed with lanthanide-labelled anti-SF antibody. Silk fibroin is coated on the nitrocellulose membrane as the test line, while goat anti-rabbit IgG antibody is coated on the membrane as the control line. As the sample solution is added to the sample pad, the sample solution will flow chromatographically along the strip and dissolve lanthanidelabelled anti-SF antibody in the fluorescent conjugate pad. Only if silk fibroin is present in the sample solution, the silk fibroin will combine with lanthanide-labelled anti-SF antibody to form a conjugate and the antigen-antibody conjugate will then flow to the test line. Silk fibroin presents in the sample would compete with silk fibroin coated on the test line in the immune reaction. If silk fibroin in the sample exceed a certain concentration (LOD), then it will combine with the lanthanidelabelled anti-SF antibody in preference to the latter. Therefore, the red mark at the test line will decrease until totally disappear. In contrast, if silk fibroin in the sample is below the LOD, an obvious red mark will appear at the test line. However, either the antigen-antibody conjugate or the lanthanidelabelled anti-SF antibody itself continues to flow to the control line and combine with goat anti-rabbit IgG antibody (secondary antibody), the control line exhibits a red mark. Generally, if both the test line and the control line appear red, the silk fibroin concentration will be below the LOD; if only the control line is red, the silk fibroin concentration will be above the LOD; and if no line is red, the test will be considered invalid. However, the test result is not only decided by the fluorescence intensity of the test line, but also influenced by recording signal of control line. For further quantitative analysis, the ratio of T/C will be applied to eliminate the effects of parameters such as the inherent heterogeneity of test strips, environmental conditions and the matrix containing the samples. In addition, the T/C ratio can eliminate the effects of immunoreaction dynamics parameters on the test and control lines, thereby shortening the interpretation time. As the silk fibroin concentration increasing, the lower the test line fluorescence intensity will be, the higher the control line fluorescence intensity will be, and thus the lower T/C ratio will be.
Page 4 of 10
considered. Lanthanide-labelled anti-SF antibodies move to the test line gradually with the prolongation of reaction time, which makes the fluorescence intensity of the test line become stronger until the end of the reaction. As shown in Fig2. (a), the fluorescence intensity of test line increased quickly during the initial stage and reached an equilibrium value after 25 min, while the T/C value decreased and finally achieved a balance. On the premise of good test results, to choose the shortest time, 25 min was obtained as the optimum immune reaction time for the following experiments. Another essential parameter that affected the fluorescence signals was the immune reaction temperature. Fig2. (b) displays the T/C values for a high concentration (120 ng/mL) of silk fibroin at different temperatures (4 °C, 10 °C, 25 °C, 37 °C, and 45 °C). With the increase of temperature, the T/C value decreased, reached its minimum at 25 °C, and then increased again. Lower or higher temperatures decrease the antibody activity and slow the specific combination of silk fibroin and antibody. Besides, lower temperatures also slow the chromatographic process, which ensures that sufficient lanthanide-labelled antibody accumulate at the test line so as to improve the accuracy of the test. Therefore, 25 °C was considered the optimum immune reaction temperature. The strip response to silk fibroin was also influenced by the pH and ionic strength of buffer solution. As shown in Fig2. (c), the T/C ratio kept a low value when the pH value increased in the range of 5.7-6.5 and then increased rapidly in the range of 6.5-7.4. The T/C ratio reached an almost constant value in the range of 7.4-10.0. Similarly, the T/C ratio increased when the ionic strength increased in the range of 0.010.05 M and then achieved a relatively smaller growth (Fig2. (d)). In our following experiments, 0.05 M PBS (pH 7.4) was used as an optimal buffer system. Sensitivity, specificity and reproducibility of the lanthanide-labelled immunochromatographic strip To achieve quantitative determination of the relationship between T/C ratio and concentration of silk fibroin, a series of concentrations was detected by the strip under optimal time and temperature. The standard curve was obtained as shown in Fig3. (a). The best linear fit for the denary logarithm of silk fibroin concentration was obtained and the equation was: T/C= -1.7726 lgC+5.4951 (R2=0.99813)
(3)
where C is the concentration of silk fibroin in ng/mL. For unknown samples, the silk fibroin concentration corresponding to the fluorescence intensity of test line can be calculated according to the standard curve, and vice versa.
Optimization of experimental parameters The experimental parameters, such as the immune reaction time, temperature, pH and ionic strength could affect the reliability and accuracy of the results; thus, establishing optimal conditions for the strip assay was necessary. As an important factor, the immune reaction time of the strip was first
The performance of the strip in terms of sensitivity was accessed by the LOD, which is known as the minimum concentration of silk fibroin that caused the disappearance of the red mark at the test line. In order to test the LOD, a total of 20 blank samples (0 ng/mL of silk fibroin in PBS, pH 7.4) were analyzed with the strip. It is easy to calculate that LOD and the
ACS Paragon Plus Environment
Page 5 of 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sensors
corresponding cut-off value of T/C ratio were 8.09 ng/m and 3.886, respectively. Whether a cross reaction with other possible interfering antigens occurs reflects the specificity of the strip. Different antigens (sericin, cotton extract, hemp extract, keratin, ovalbumin, collagen, HSA and silk fibroin) were assayed using the strip. As shown in Fig3. (b), only the silk fibroin revealed a positive result (T/C value3.886). Furthermore, the T/C values between silk fibroin and other samples greatly differed, which also indicated that this lanthanide-labelled immunochromatographic strip has high specificity for detecting silk fibroin. The coefficient of variations and recoveries of different concentrations (40, 60, 80, 100 and 120 ng/mL) of silk fibroin were determined by the strip, based on the calculated concentrations obtained from the standard curve. As shown in Fig4. and Table 1, the coefficients of variation were in the range of 6.3~19.75%, and recoveries varied from 94.15% to 102.55%, confirming the high precision and reproducibility of the strip. Identification of archaeological samples
used immunoassay in the field of archaeology. In comparison with ELISA, IFM based on the collection of images showing the distribution of fluorescent molecules can visualize the target protein in embedded cross-section in situ.23a However, the complicated pre-treatment procedure, expensive equipment and need for qualified expert confine these techniques to the laboratory environment. In contrast, the lateral flow immunoassay has superiority of on-site testing due to its unique advantages. Nevertheless, the LOD of ancient silk using colloidal gold-based strip is approximately 1.5 µg/mL, which is lower than that of other immunoassays.20 A higher sensitivity is often required in the diagnostic testing of ancient silk traces. As a consequence, the combination of fluorescent label probe and immunochromatographic strip is undoubtedly one of the best choices. The lanthanide-labelled immunochromatographic strip is especially suitable for the identification of poor preserved ancient silks (severely degraded) or even the silk traces, which is also the key challenge in archaeological site. For the silk traces, a little amount of mud or a drop of coffin liquid can meet the demand of rapid and point-of-care test. This is very convenient and useful in the archaeological sites. Conclusion
Three archaeological samples were extracted following the above-mentioned methods and prepared as 100 ng/mL solutions using PBS (pH 7.4). PBS and silk fibroin solutions (100 ng/mL) were used as negative and positive controls, respectively. All solutions were loaded on the sample pad and assayed with the lanthanide-labelled immunochromatographic strip. Fig5. (a) shows the image of the strips under UV irradiation at a wavelength of 365 nm. For PBS and sample A (wool fragment from Kazakhstan), fluorescence bands appeared in both the test line and the control line. In contrast, for samples B, sample C and silk fibroin, no band appeared in the test line. This indicated that the lanthanide-labelled immunochromatographic strip was highly specific toward ancient silk. To quantitatively investigate the fluorescence responses of the immunosensor with different ancient samples, the fluorescence intensity of the test line and control line was quantified with a portable fluorospectrophotometer. As shown in Fig5. (b), the average T/C value for sample A was 4.108, which was significantly higher than the cut-off value, demonstrating no antigen (silk fibroin) was specifically recognized by the strip assay. In contrast, the average T/C values for sample B and sample C were 2.65 and 2.532, respectively, clearly indicating the presence of antigen in the samples. Moreover, their corresponding concentrations calculated from standard curve were 40.28 and 46.97 ng/mL, respectively. Both the qualitative and quantitative results confirmed that the lanthanide-labelled immunochromatographic strip could identify silk from different types of archaeological fabrics effectively and accurately.
In the present study, a portable, rapid, sensitive and pointof-care lanthanide-labelled immunochromatographic strip assay was developed to detect ancient silks. The strip shows much higher analytical sensitivity and better quantitative discrimination in comparison with colloidal gold-based immunochromatographic strip. No cross-reactions with other possible interfering antigens were observed. Besides, the strip also shows good reproducibility. Thus, this strip assay may provide a new protocol for identifying the origin, transmission and exchange of silk. Moreover, this strip system is versatile and can be easily extended to the analysis of other archaeological proteinaceous materials by utilizing other lanthanide-labelled antibodies. Consequently, the lanthanide-labelled immunochromatographic strip assay has the potential to be a powerful tool for the on-site detection in the archaeological field.
Comparison with ELISA, IFM and colloidal gold-based strips Generally, both the ELISA and IFM techniques show high sensitivity and specificity. ELISA is the most commonly
ACS Paragon Plus Environment
ACS Sensors
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 10
Fig1. (a) Digital images of archaeological fabric samples. Sample A: wool fragment from Kazakhstan; Sample B: silk fragment from the Chu period tomb in Anji County, Zhejiang Province; Sample C: silk fragment from the Song period tomb in Yuyao City, Zhejiang Province. (b) Schematic diagram of the lanthanide-labelled immunochromatographic strip.
Fig2.Optimization of the parameters of the lanthanide-labelled immunochromatographic strip assay. (a) T/C ratio vs. immunoreaction time; (b) T/C ratio vs. immunoreaction temperature; (c) T/C ratio vs. pH; (d) T/C ratio vs. ionic strength.
ACS Paragon Plus Environment
Page 7 of 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sensors
Fig3. (a) Immunochromatographic strip standard curves obtained at optimized immunoreaction time, temperature and buffer system. (b) Typical fluorescence responses of the lanthanide-labelled immunochromatographic strip assay with possible interfering antigens.
Fig5. (a) Image and (b) T/C ratio of the lanthanide-labelled immunochromatographic strips prepared using negative control (PBS), positive control (silk fibroin) and archaeological samples. Sample A: wool fragment from Kazakhstan; Sample B: silk fragment from the Chu period tomb in Anji County, Zhejiang Province; Sample C: silk fragment from the Song period tomb in Yuyao City, Zhejiang Province. The image was taken under UV irradiation at a wavelength of 365 nm.
Fig4. Data plots of assay variability tests using silk fibroin at five different concentrations.
ACS Paragon Plus Environment
ACS Sensors
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Table 1 Coefficients of variation and recoveries of different concentrations of silk fibroin. C
CV a (%)
Recovery
T/C
۱∗
40
2.636
41.02
10.06
102.55
60
2.402
56.49
5.22
94.15
80
2.107
81.47
17.57
101.84
100
1.976
95.94
16.75
95.94
120
1.816
119.12
11.80
99.27
(ng/mL)
b
(%)
a
CV=T/CS.D. ⁄ T/Cmean×100%
b
Recovery=C*/ C×100% (C*was calculated from the standard curve.)
ACKNOWLEDGMENT Financial support was provided by the National Natural Science Foundation of China (51603188), the Public Technology Research Plan of Zhejiang Province, China under Grant No. 2016C33175 and Science Foundation of Zhejiang Sci-Tec University (ZSTU) under Grant No. 13012141-Y.
ABBREVIATIONS SF, silk fibroin, LOD, limit of detection.
REFERENCES 1. Sun, W.; Yu, H. S.; Shen, Y. H.; Banno, Y.; Xiang, Z. H.; Zhang, Z., Phylogeny and evolutionary history of the silkworm. Science China-Life Sciences 2012, 55 (6), 483-496. 2. Glausiusz, J., Traveling the Silk Road: Ancient Pathway to the Modern World. Nature 2009, 462 (7273), 574-574. 3. (a) Li, M. Y.; Zhao, Y.; Tong, T.; Hou, X. H.; Fang, B. S.; Wu, S. Q.; Shen, X. Y.; Tong, H., Study of the degradation mechanism of Chinese historic silk (Bombyx mori) for the purpose of conservation. Polymer Degradation And Stability 2013, 98 (3), 727735; (b) Vilaplana, F.; Nilsson, J.; Sommer, D. V. P.; Karlsson, S., Analytical markers for silk degradation: comparing historic silk and silk artificially aged in different environments. Analytical And Bioanalytical Chemistry 2015, 407 (5), 1433-1449; (c) Zhang, X. M.; Berghe, I. V.; Wyeth, P., Heat and moisture promoted deterioration of raw silk estimated by amino acid analysis. Journal Of Cultural Heritage 2011, 12 (4), 408-411. 4. (a) Ball, P., Rethinking silk's origins. Nature, 2009, DOI: 10.1038/457945a; (b) Good, I. L.; Kenoyer, J. M.; Meadow, R. H., New Evidence for Early Silk in the Indus Civilization. Archaeometry 2009, 51, 457-466. 5. Liu, J.; Guo, D. H.; Zhou, Y.; Wu, Z. Y.; Li, W. Y.; Zhao, F.; Zheng, X. M., Identification of ancient textiles from Yingpan, Xinjiang, by multiple analytical techniques. Journal Of Archaeological Science 2011, 38 (7), 1763-1770.
Page 8 of 10
6. Margariti, C.; Protopapas, S.; Orphanou, V., Recent analyses of the excavated textile find from Grave 35 HTR73, Kerameikos cemetery, Athens, Greece. Journal Of Archaeological Science 2011, 38 (3), 522-527. 7. (a) Okayama, M.; Sato, M.; Akada, M., Basic Studies on the Identification of Excavated Archaeological Textile Fibers Using Polarized FT-IR Micro-Spectroscopy [II] - The Investigation of the Infrared Dichroism of Ramie. Sen-I Gakkaishi 2014, 70 (1), 14-18; (b) Zhang, X. M.; Wyeth, P., Using FTIR spectroscopy to detect sericin on historic silk. Science China-Chemistry 2010, 53 (3), 626631. 8. Lee, J.; Ceglia, A.; Kim, K. J.; Lee, Y., Characterization of dyed textiles using TOF-SIMS and FT-IR. Surface And Interface Analysis 2012, 44 (6), 653-657. 9. Idone, A.; Gulmini, M.; Henry, A. I.; Casadio, F.; Chang, L. R.; Appolonia, L.; Van Duyne, R. P.; Shah, N. C., Silver colloidal pastes for dye analysis of reference and historical textile fibers using direct, extractionless, non-hydrolysis surface-enhanced Raman spectroscopy. Analyst 2013, 138 (20), 5895-5903. 10. (a) Chen, L.; Wang, Z.; Ferreri, M.; Su, J.; Han, B., Cephalexin residue detection in milk and beef by ELISA and colloidal gold based one-step strip assay. Journal of agricultural and food chemistry 2009, 57 (11), 4674-4679; (b) Heginbotham, A.; Millay, V.; Quick, M., The Use of Immunofluorescence Microscopy and Enzyme-Linked Immunosorbent Assayas Complementary Techniques for Protein Identification in Artists' Materials. Journal of the American Institute for Conservation 2006, 45 (2), 89-105; (c) Palmieri, M.; Vagnini, M.; Pitzurra, L.; Brunetti, B. G.; Cartechini, L., Identification of animal glue and hen-egg yolk in paintings by use of enzyme-linked immunosorbent assay (ELISA). Analytical and bioanalytical chemistry 2013, 405 (19), 6365-71; (d) Palmieri, M.; Vagnini, M.; Pitzurra, L.; Rocchi, P.; Brunetti, B. G.; Sgamellotti, A.; Cartechini, L., Development of an analytical protocol for a fast, sensitive and specific protein recognition in paintings by enzymelinked immunosorbent assay (ELISA). Analytical and bioanalytical chemistry 2011, 399 (9), 3011-23; (e) Potenza, M.; Sabatino, G.; Giambi, F.; Rosi, L.; Papini, A. M.; Dei, L., Analysis of egg-based model wall paintings by use of an innovative combined dot-ELISA and UPLC-based approach. Anal Bioanal Chem 2013, 405 (2-3), 691701; (f) Vagnini, M.; Pitzurra, L.; Cartechini, L.; Miliani, C.; Brunetti, B. G.; Sgamellotti, A., Identification of proteins in painting crosssections by immunofluorescence microscopy. Analytical and bioanalytical chemistry 2008, 392 (1-2), 57-64; (g) Cartechini, L.; Vagnini, M.; Palmieri, M.; Pitzurra, L.; Mello, T.; Mazurek, J.; Chiari, G., Immunodetection of proteins in ancient paint media. Accounts of chemical research 2010, 43 (6), 867-876. 11. (a) Bailly, M. L.; Gonçalves, M. L.; Harter-Lailheugue, S.; Prodéo, F.; Araujo, A.; Bouchet, F., New finding of Giardia intestinalis (Eukaryote, Metamonad) in Old World archaeological site using immunofluorescence and enzyme-linked immunosorbent assays. Mem Inst Oswaldo Cruz, Rio de Janeiro 2008, 103 (3), 298300; (b) Bailly, M. L.; Gonçalves, M. L.; Lefèvre, C.; Roper, D. C.; Pye, J. W.; Araujo, A.; Bouchet, F., Parasitism in Kansas in the 1800s – A glimpse to the past through the analysis of grave sediments from Meadowlark cemetery. Mem Inst Oswaldo Cruz, Rio de Janeiro 2006, 101(Suppl. II), 53-56. 12. (a) Kang, K. R.; Dzakah, E. E.; Huang, Y. P.; Xie, M. Q.; Luo, X. C.; Li, W. M.; Wang, J. H., Development and performance evaluation of a novel immunofluorescence chromatographic assay for histidine-rich protein 2 of Plasmodium falciparum. Malaria Journal 2015, 14; (b) Oshiro, S.; Tada, T.; Kameoka, Y.; Suzuki, K.; Ohmagari, N.; Miyoshi-Akiyama, T.; Kirikae, T., Development and evaluation of immunochromatography to detect Gram-negative bacteria producing ArmA 16S rRNA methylase responsible for aminoglycoside resistance. Journal Of Microbiological Methods 2015, 118, 159-163; (c) Vyas, S. S.; Jadhav, S. V.; Majee, S. B.; Shastri, J. S.; Patravale, V. B., Development of immunochromatographic strip test using fluorescent, micellar silica
ACS Paragon Plus Environment
Page 9 of 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sensors
nanosensors for rapid detection of B-abortus antibodies in milk samples. Biosensors & Bioelectronics 2015, 70, 254-260. 13. (a) Wang, Y. L.; Wang, L. M.; Wang, S. Y.; Yang, M. M.; Cai, J.; Liu, F. Q., ‘Green’ immunochromatographic electrochemical biosensor for mercury(II). Microchimica Acta 2016, 183 (9), 25092516; (b) Wang, L. M.; Lu, D. L.; Wang, J.; Du, D.; Zou, Z. X.; Wang, H.; Smith, J. N.; Timchalk, C.; Liu, F. Q.; Lin, Y. H., A novel immunochromatographic electrochemical biosensor for highly sensitive and selective detection of trichloropyridinol, a biomarker of exposure to chlorpyrifos. Biosens Bioelectron 2011, 26 (6), 2835-40. 14. (a) Gao, H. F.; Han, J.; Yang, S. J.; Wang, Z. X.; Wang, L.; Fu, Z. F., Highly sensitive multianalyte immunochromatographic test strip for rapid chemiluminescent detection of ractopamine and salbutamol. Anal Chim Acta 2014, 839, 91-6; (b) Wang, W. W.; Su, X. X.; Ouyang, H.; Wang, L.; Fu, Z. F., A novel immunochromatographic assay based on a time-resolved chemiluminescence strategy for the multiplexed detection of ractopamine and clenbuterol. Anal Chim Acta 2016, 917, 79-84. 15. (a) Guo, D. L.; Pan, Q. W.; Li, K. P.; Li, J. Q.; Shen, H. W.; Wang, X. L.; Zhang, X. Y.; Li, X. S.; Fu, F.; Feng, L.; Li, X., Development and clinical evaluation of a new goldimmunochromatographic assay for the detection of antibodies against field strains of pseudorabies virus. Journal Of Virological Methods 2015, 222, 164-169; (b) Kim, Y. R.; Park, S. B.; Fagutao, F. F.; Nho, S. W.; Jang, H. B.; Cha, I. S.; Thompson, K. D.; Adams, A.; Bayley, A.; Jung, T. S., Development of an immunochromatography assay kit for rapid detection of ranavirus. Journal Of Virological Methods 2015, 223, 33-39. 16. Zhou, C. N.; Zhang, X. Y.; Huang, X. X.; Guo, X. S.; Cai, Q.; Zhu, S. M., Rapid Detection of Chloramphenicol Residues in Aquatic Products Using Colloidal Gold Immunochromatographic Assay. Sensors 2014, 14 (11), 21872-21888. 17. (a) Peng, J.; Wang, Y. W.; Liu, L. Q.; Kuang, H.; Li, A. K.; Xu, C. L., Multiplex lateral flow immunoassay for five antibiotics detection based on gold nanoparticle aggregations. Rsc Advances 2016, 6 (10), 7798-7805; (b) Chen, Y. N.; Wang, Y. W.; Liu, L. Q.; Wu, X. L.; Xu, L. G.; Kuang, H.; Li, A. K.; Xu, C. L., A gold immunochromatographic assay for the rapid and simultaneous detection of fifteen β-lactams. Nanoscale 2015, 7 (39), 16381; (c) Kong, D. Z.; Liu, L. Q.; Song, S. S.; Suryoprabowo, S.; Li, A. K.; Kuang, H.; Wang, L. B.; Xu, C. L., A gold nanoparticle-based semiquantitative and quantitative ultrasensitive paper sensor for the detection of twenty mycotoxins. Nanoscale 2016, 8 (9), 5245. 18. Wang, C. K.; Liu, D. J.; Wang, Z. X., Gold nanoparticle based dot-blot immunoassay for sensitively detecting Alzheimer's disease related beta-amyloid peptide. Chemical Communications 2012, 48 (67), 8392-8394. 19. (a) Liu, X.; Xiang, J. J.; Tang, Y.; Zhang, X. L.; Fu, Q. Q.; Zou, J. H.; Lin, Y. H., Colloidal gold nanoparticle probe-based immunochromatographic assay for the rapid detection of chromium ions in water and serum samples. Analytica Chimica Acta 2012, 745, 99-105; (b) Xing, C. R.; Liu, L. Q.; Song, S. S.; Feng, M.; Kuang, H.; Xu, C. L., Ultrasensitive immunochromatographic assay for the simultaneous detection of five chemicals in drinking water. Biosensors & Bioelectronics 2015, 66 (66C), 445. 20. Liu, M. M.; Li, Y.; Zheng, H. L.; Zhou, Y.; Wang, B.; Hu, Z. W., Development of a gold-based immunochromatographic strip assay for the detection of ancient silk. Analytical Methods 2015, 7 (18), 7824-7830. 21. Majdinasab, M.; Sheikh-Zeinoddin, M.; Soleimanian-Zad, S.; Li, P. W.; Zhang, Q.; Li, X.; Tang, X. Q.; Li, J., A reliable and sensitive time-resolved fluorescent immunochromatographic assay (TRFICA) for ochratoxin A in agro-products. Food Control 2015, 47, 126-134. 22. Zhang, F.; Zou, M. Q.; Chen, Y.; Li, J. F.; Wang, Y. F.; Qi, X. H.; Xue, Q., Lanthanide-labeled immunochromatographic strips for the rapid detection of Pantoea stewartii subsp stewartii. Biosensors & Bioelectronics 2014, 51, 29-35.
23. (a) Liu, M. M.; Xie, J.; Zheng, H. L.; Zhou, Y.; Wang, B.; Hu, Z. W., Identification of Ancient Silk Using an Enzyme-linked Immunosorbent Assay and Immuno-fluorescence Microscopy. Analytical Sciences 2015, 31 (12), 1317-1323; (b) Zheng, Q.; Wu, X.; Zheng, H.; Zhou, Y., Development of an enzyme-linkedimmunosorbent-assay technique for accurate identification of poorly preserved silks unearthed in ancient tombs. Anal Bioanal Chem 2015, 407 (13), 3861-7.
ACS Paragon Plus Environment
ACS Sensors
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 10 of 10
For TOC only
ACS Paragon Plus Environment
10
