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A Graphene-Silver Nanoparticles-Silicon Sandwich SERS Chip for Quantitative Detection of Molecules and Capture, Discrimination, Inactivation of Bacteria Xinyu Meng, Houyu Wang, Na Chen, Pan Ding, Huayi Shi, Xia Zhai, Yuanyuan Su, and Yao He Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b05139 • Publication Date (Web): 02 Apr 2018 Downloaded from http://pubs.acs.org on April 2, 2018
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Analytical Chemistry
Xinyu Meng,‡ Houyu Wang,‡ Na Chen, Pan Ding, Huayi Shi, Xia Zhai, Yuanyuan Su and Yao He* Laboratory of Nanoscale Biochemical Analysis, Institute of Functional Nano & Soft Materials (FUNSOM), and Collaborative Innovation Center of Suzhou Nano Science and Technology (NANO−CIC), Soochow University, Suzhou, Jiangsu 215123, China *E-mail:
[email protected]; Fax: 86-512-65880946.
ABSTRACT: There currently exists increasing concerns on the development of a kind of high-performance SERS platform, which is suitable for sensing applications ranging from molecular to cellular (e.g., bacteria) level. Herein, we develop a novel kind of universal SERS chip, made of graphene (G)-silver nanoparticles (AgNPs)-silicon (Si) sandwich nanohybrids (G@AgNPs@Si), in which AgNPs are in situ grown on silicon wafer through hydrofluoric acid-etching assisted chemical reduction, followed by coating with a single-layer graphene via polymer-protective etching method. The resultant chip features strong, stable, reproducible surface-enhanced Raman scattering (SERS) effect, and reliable quantitative capability. By virtues of these merits, the G@AgNPs@Si platform is capable for not only molecular detection, quantification but also cellular analysis in real systems. As a proof-of-concept application, the chip allows ultrahigh sensitive and reliable detection of adenosine triphosphate (ATP), with detection limit of ~1 pM. In addition, the chip, served as novel multifunctional platform, enables simultaneous capture, discrimination, and inactivation of bacteria. Typically, the bacterial capture efficiency is 54% at 108 CFU mL-1 bacteria, and the antibacterial rate reaches 93% after 24-h treatment. Of particular note, Escherichia coli and Staphylococcus aureus spiked into blood can be readily distinguished via the chip, suggesting its high potential for clinical applications.
able for quantitative SERS analysis, there currently exists increasing concerns on the development of novel universal SERS platform, which can serve not only as a powerful molecular quantitative tool, but also as a cellular “workstation” integrated with multiple functions, such as multimodal imaging, simultaneous diagnosis and therapy, simultaneous capture, profiling and mapping of live cells, and simultaneous capture, monitor and elimination of pathogen, etc.10, 11 However, such universal SERS platform remains vacant, and has fueled a continual and urgent research up to present.
INTRODUCTION Surface-enhanced Raman scattering (SERS) has attracted extensive attentions in various fields ascribed to its extraordinary features since its discovery in 1974.1,2 Remarkably, it can boost inherently feeble Raman signals by several orders of magnitude when molecules are located at “hot spots”, holding great promise for myriad ultrasensitive sensing and analysis applications.3,4 Nevertheless, suffered from the relatively poor reproducibility and stability of SERS signals, it is challenging to fulfill reliable quantitative SERS analysis.5,6 To date, tremendous efforts have been made to improve SERS quantitative capability, particularly focusing on three aspects: (1) introduction of internal standard (IS); (2) fabrication of highlyordered SERS substrates; (3) introduction of inert shell shielded SERS substrates from external interferences (e.g., oxidation and corrosion). With regard to the first aspect, IS species share similar SERS enhancement as the analytes, and thus the ratiometric signal of analyte intensity to IS intensity can be employed for calibrating inhomogeneous electromagnetic enhancement.7-9 However, IS species employed in most current SERS systems are still suffered from the disturbances originated from the reactions between naked metal nanoparticles and contacted IS species, including chemical adsorption, charge transfer, photo-induced damage and metal-assisted catalysis.8 On the other side, even these approaches are work-
As for the second aspect, various high-quality SERS substrates with relatively uniform and controllable hot spots have been developed, which are generally made of highly ordered metal NPs decorated or dispersed on a flat solid support (e.g., quartz, Si, Pt, etc.).12-14 In particular, silicon nanohybridsbased SERS substrates made of noble metal nanoparticles in situ growth on silicon wafer surface not only preserve adaptable reproducibility (e.g., the value of relative standard deviation (RSD) is generally less than 15%) but also display good SERS enhancement (e.g., enhancement factor (EF): ~1056 15,16 ). The adaptable reproducibility is originated from homogeneous metallic NPs tightly anchored on the silicon surface, thus preventing the uncontrollable aggregation of free metal NPs in liquid phase.13,14 Additional SERS enhancement is
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Figure 1. Schematic illustration of fabrication of the G@AgNPs@Si chip, with an area of 0.7 × 1.0 cm2. The SERS mapping spectra of the G@AgNPs@Si collected from 50 random spots on the surface of chip (excitation wavelength = 633 nm, acquisition time = 1 sec, laser power = 20 mW). stemmed from both metal NPs-scattered electromagnetic field and semiconducting silicon reflected electromagnetic field.17-19 As a consequence, silicon-based nanohybrids have been designed and fabricated as high-efficacy SERS sensors for the determination of chemical and biological species.13,14,16,20 However, until now, the lack of proper IS signals in such SERS systems confines their applications to qualitative or/and semi-quantitative analysis. Moreover, metal NPs contained in the nanohybrids are prone to be oxidized, which is adverse to the stability of SERS signals.
note, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) spiked into blood can be discriminated via the developed chip. EXPERIMENTAL SECTION Preparation of AgNPs@Si. The silicon nanohybrids SERS chip (AgNPs@Si) was fabricated based on hydrofluoric acid (HF)-etching assisted chemical method. First, the silicon wafer was washed with Milli-Q water (Millipore) for 3 times to remove dust and aqueous impurities, and then cleaned with acetone by ultrasonic treatment for 10 min. Afterwards, a strong oxidant solution containing H2SO4 (98%) and H2O2 (30%) (a volume ratio of 3:1) was used for cleaning silicon wafer for 30 min and then silicon wafer was rinsed in ultrapure water for 3 times to fully remove organic residue. Next, the clean silicon wafer was treated by 5% hydrogen fluoride (HF) aqueous solution for 30 min to form Si-H bonds. Finally, the treated silicon wafer was immersed in 2 mM silver nitration solution containing 10% HF with slow stirring for 30 min to in situ grow AgNPs on silicon wafer.
On the other hand, graphene, which is a honeycomb lattice crystalline structure consisting of sp2 hybridized carbon,21,22 possesses unique merits in SERS applications: (i) extra SERS enhancement attributed to excellent electronic transmission effect of graphene, which belongs to chemical enhancement mechanism;23-25 (ii) an inert shield to protect metal NPs from external interferences;26,27 (iii) intrinsic peak of 2670 cm-1 located in the Raman silent zone, which can be employed as the desirable IS to correct SERS intensities;28,29 (iv) abundant delocalized π bonds and good biocompatibility, served as a driving force to capture probe molecules with aromatic structures for sensing applications.30-32 However, the relatively lower EF of graphene-enhanced Raman scattering (GERS) (e.g., EF:
