Fabrication of Miniature Surface Plasmon Resonance Sensor Chips

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Applications of Polymer, Composite, and Coating Materials

Fabrication of miniature surface plasmon resonance sensor chips by using confined sessile drop technique Supeera Nootchanat, Wisansaya Jaikeandee, Patrawadee Yaiwong, Chutiparn Lertvachirapaiboon, Kazunari Shinbo, Keizo Kato, Sanong Ekgasit, and Akira Baba ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b01617 • Publication Date (Web): 07 Mar 2019 Downloaded from http://pubs.acs.org on March 16, 2019

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ACS Applied Materials & Interfaces

Fabrication of Miniature Surface Plasmon Resonance Sensor Chips by Using Confined Sessile Drop Technique Supeera Nootchanat†, Wisansaya Jaikeandee†‡ , Patrawadee Yaiwong†§, Chutiparn Lertvachirapaiboon†, Kazunari Shinbo†, Keizo Kato†, Sanong Ekgasit‡, and Akira Baba*† †Graduate

School of Science and Technology, Niigata University 8050 Ikarashi 2-nocho, Nishi-

ku, Niigata, 959-2181, Japan. ‡Sensor

Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University,

Bangkok 10330, Thailand. §

Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai, Thailand.

KEYWORDS. miniatuire SPR sensor ship, confined sessile drop technique, NOA61 hemispherical prism, PDMS, 3D-print flow cell

ACS Paragon Plus Environment

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ABSTRACT. In this study, we demonstrate a simple and efficient method to fabricate miniature surface plasmon resonance (SPR) sensor chips by using confined sessile drop technique. A liquid optical adhesive (NOA 61) was dropped on the circular flat surface of cylindrical substrates made of polydimethylsiloxane (PDMS). The formation of hemispherical optical prisms was accomplished by taking advantage of the sharp edges of cylindrical PDMS substrates that prevented the overflow of liquid NOA 61 at the edge of substrates. The size of the hemispherical optical prisms can be controlled by changing the diameter of the cylindrical PDMS substrates. After UV curing, the SPR sensor chips were obtained by the deposition of 3-nm-thick chromium and 47-nm-thick gold on the flat side of the prisms. The fabricated miniature SPR sensor chips were then mounted on a 3D-printed flow cell to complete the microfluidic SPR sensor module. The miniature SPR sensor chips provided a comparable sensitivity to the conventional high refractive index glass SPR chips. To demonstrate the detection capability of nanometer-sized materials, we applied the miniature microfluidic SPR system for monitoring the deposition of layer-by-layer ultrathin films of poly(diallyldimethylammonium chloride)/poly(sodium 4styrenesulfonate) and for detecting human immunoglobulin G.

1. INTRODUCTION Surface plasmon resonance (SPR) spectroscopy is a technique that has a powerful ability to detect and provide real-time information of probe molecules deposited on thin metal films.1-3 SPR has become a popular optical biosensing phenomenon that is widely used in the fields of biochemistry, biology, and medical science.2-9 Since the 1990s, when SPR was first used for studying


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biomolecules,6,

9-10

it has been extensively applied to investigate the association of proteins,3

antigen-antibody interactions,6, 11-13 DNA-drug bindings,14 and carbohydrate-RNA interactions15. Furthermore, SPR technology has been recently adapted into a plottable SPR platform in which a smartphone is coupled with special custom-design optics. The plottable SPR system could be applied for the biochemical detection16-17 and adsorption of proteins.18 The devices could be applied to point-of-care SPR devices that can be used at point-of-need anytime outside laboratories.19 In principle, an SPR biosensor works based on the change of local reflective index at the liquidsolid interface caused by the adsorption of analytes on recognized biomolecules immobilized on thin metal film surface.6,

20-21

A conventional SPR biosensor is performed based on the

Kretschmann configuration in which optical prisms are used to couple the incident light at attenuated total reflectance (ATR) for the excitation of SPR.1, 9, 21-22 When SPR is excited, a marked decline of reflected light intensity is observed as a dip in reflection spectrum recorded as a function of wavelength or incident light angule.23 The change of local reflective index of dielectric medium results in the shift of SPR dips with exceptional reflective index sensitivity.21, 23-26 Use of highquality optics and expensive disposable SPR chips is preferred in most conventional SPR systems. However, the expensive instrumental system limits the wide range of applications such as for use in private hospitals, point-of-care tests, and so on. To reduce the cost of expensive optics, compact SPR apparatus9, 27-29 and use of polymeric optical prisms30-32 are proposed as alternative SPR systems. The compact design of the SPR system can reduce the complexity of traditional prism-based SPRs. However, it requires the understanding and specialization of technical skills in optics. A polymeric prism can directly replace the highquality prism in conventional SPR setup. Deposition of thin metal films on polymeric prisms can


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also produce low-cost prism-sensor chip and allow disposable uses. However, the fabrication of polymeric prisms for SPR applications still requires specific-design molds31-32 or highperformance and expensive 3D printers.30 Nevertheless, surface polishing is essential to improve surface smoothness and reduce light scattering of plastic SPR prisms.30 The elimination of the use of mold and surface refining would improve the fabrication and use of polymeric prisms in SPR applications. We previously reported the fabrication of small-sized PDMS plano-convex lens using confined sessile drop techniqe.33 In this work, we extend the use of the confined sessile drop technique as a facile method for fabricating miniature optical prisms for SPR coupling. The developed method delivers distinctive advantages, including the simple, low-cost, and non-template approach, for manufacturing polymeric optical prisms with controllable sizes. Sessile droplets of Norland Optical Adhesive 61 (NOA 61) were formed on circular substrates made of polydimethylsiloxane (PDMS) and cured under UV exposure to create hemispherical optical prisms. Unlike conventional manufacturing of optical components, the surface of the fabricated prism can be optically smooth without any additional surface refinement, providing ready-to-use high-quality optical component. SPR sensor chips were fabricated by the deposition of thin metal films on the planar side of the prism. The assembly of miniature SPR sensor chips to a 3D-pritned flow cell created a complete microfluidic SPR analytical system with exceptional reflective index sensitivity. With an appropriate design, the developed microfluidic SPR system requires the sample solution of just a few hundred microliters, which is suitable for miniature chemical analysis. To demonstrate a detection capability of nanometer-sized materials, we applied the miniature microfluidic SPR system for monitoring the deposition of PDADMAC/PSS layer-by-layer (LbL) ultrathin films and for detecting human immunoglobulin G (IgG).


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2. EXPERIMENTAL SECTION 2.1 Materials and chemical reagents. NOA 61 was purchased from Norland Products Inc. Sylgard® 184 silicone elastomer was purchased from Dow Corning Toray Corporation. 11Mercaptoundecanoic acid (11-MUA), phosphate buffered saline (PBS, pH 7.4), monoclonal antihuman IgG (Fab specific) antibody produced in goat, IgG from human serum, Nhydroxysuccinimide

(NHS),

ethanolamine

dimethylaminopropyl)-carbodiimide

hydrochloride

hydrochloride

(EDC),

(EA-HCl),

1-ethyl-3-(3-

sodium

3-mercapto-1-

propanesulfonate (MPS), poly(diallyldimethylammonium chloride) solution (PDADMAC, M w = ~200,000–350,000) and poly(sodium 4-styrenesulfonate) (PSS, Mw = 70,000) were purchased from Sigma-Aldrich Inc. All chemicals were used as received without additional purification.

2.2 Fabrication of SPR sensor chips.

The fabrication of SPR sensor chips included the

following steps: (1) preparation of circular PDMS substrates, (2) fabrication of polymeric optical prisms, and (3) formation of metal films (Figure S1). To form circular PDMS substrates, the mixture of PDMS elastomer base and curing agent (weight ratio of 10:1) was casted on a flatbottomed mold followed by degassing in a vacuum chamber for 3 h. Subsequently, after slow curing at 30 °C for 12 h, PDMS sheets with the thickness of ~0.6 mm were obtained. Circular PDMS substrates were shaped by hollow punchers. The diameter of circular PDMS substrates can be varied by changing the size of hollow punchers (2.5–6 mm) (Figure S1A). To fabricate polymeric hemispherical prisms, liquid NOA 61 was dropped onto the surfaces of circular PDMS substrates. The spreading of liquid photopolymer droplets stopped at the edge of the PDMS substrates. Additional liquid polymers were gradually added to the droplets until the


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contact angles at the edge of the PDMS substrates reached 90°. To confirm that the liquid polymer completely stops, the droplets were left for 30 min before curing under UV light for 1 h (Figure S1B). Note that the diameters of prisms could be changed by changing the diameters of circular PDMS substrates. After curing, PDMS substrates were peeled off from the polymeric hemispherical prisms. The layers of 3 nm Cr and 47 nm gold films were created on the planar side of the polymeric prisms by thermal evaporation to create the miniature SPR sensor chips with the Kretschmann configuration (Figure S1C). Kretschmann configuration is well-known prismcoupling approach to excite SPR.9 The fabricated miniature SPR sensor chips were later mounted on flow cells fabricated by a 3D printer. 2.3 Formation of PDADMAC/PSS bilayers on the surfaces of SPR sensor chips.

The

formation of PDADMAC/PSS bilayers on the surface of SPR sensor chips was accomplished by using LbL deposition technique. The SPR chip was immersed in an aqueous solution of MPS (1 mM) overnight. After rinsing with DI water, the LbL deposition was performed. The sensor chip was immersed in the PDADMAC solution (20 wt.% in DI water) for 15 min and rinsed with DI water for 2 min. The sensor chip was then immersed in PSS (1 mg/mL in DI water) for 15 min and rinsed with DI water for 2 min to complete a bilayer of PDADMAC/PSS. The LbL deposition process was repeated to create 2, 4, 6, 8, and 10 bilayers of PDADMAC/PSS on the surface of the sensor chip. 2.4 Characterizations.

The surface morphology was characterized using an atomic force

microscope (SPM-9600, Shimadzu cooperation, Japan). The wavelength-modulated SPR characterization was performed with a home-built SPR setup. The white light from a halogen source (HL-2000, Ocean Optics, USA) was coupled through a 600-μm optical fiber (F600-UVVisSR, StellarNet Inc, USA) and was collimated using a collimating lens (74-VIS, Ocean Optics,


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USA). The light beam was passed through a linear polarizer, an aperture (diameter, 0.7 mm), and a biconvex lens with a focal length of 150 mm. The sample was mounted on a θ-2θ motorized goniometer. The reflected light was collected to a 600-μm optical fiber (F600-UVVis-SR, StellarNet Inc, USA) using a plano-convex lens with focal length of 12 mm and a collimating lens (74-VIS, Ocean Optics, USA) and recorded by a UV-VIS spectrometer (USB 4000, Ocean Optics, USA). OP Wave software was utilized for all characterization and data processing. All 3D printed holders and flow cells coupled to SPR chips were printed using a 3D printer (Ultimaker 3, Ultimaker B.V., Netherlands).

3. RESULTS AND DISCUSSION To create hemispherical SPR sensor chips, we first fabricated hemispherical optical prisms using NOA 61 as a sole material. When liquid NOA 61 was dispensed on a PDMS sheet with flat surface, a droplet of liquid polymer with a hemispherical shape was formed and gradually spread out from the center driven by interfacial tension and gravitational force.33 The spreading of the liquid polymer continued with the symmetric expansion of the spreading diameter and stopped after reaching the equilibrium. Figure S2A shows a liquid NOA 61 droplet of 20 µL on PDMS surface. Although the spreading of the liquid polymer on PDMS surface completely stopped at the first 30 min, the photograph was taken 24 h after the liquid dispersion. The result clearly reveals the formation of somewhat hemispherical liquid NOA 61 with a diameter of 4.7 mm on PDMS surface with an equilibrium (thermodynamic) contact angle (θe) of 50°. When the volume of the liquid NOA 61 was increased from 20 to 60 µL, the diameter of the hemispherical droplet was increased from 4.7 to 7.4 mm without a significant change of the θe value as shown in Figure S2B. Although the hemispherical droplet can be formed by directly dispensing the liquid polymer on the semi-


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infinite flat surface of the PDMS substrate, the control ability and repeatability are not present. Hence, a hemispherical optical prism for SPR applications with a precise diameter cannot be obtained on the semi-infinite flat surface of the PDMS substrate. To fabricate highly controllable, reproducible and efficient hemispherical optical prisms, we performed the confined sessile drop technique by dropping liquid polymer onto the circular flat surface of the cylindrical PDMS substrate. We used the edge effect in wetting to inhibit the spreading of the liquid polymer over the sharp edge and the spilling to the side of a pedestal/column.33-35 When liquid NOA 61 was dropped on the PDMS substrate with a specific diameter (2.5-6 mm), the liquid polymer gradually spread out from the center and stopped at the edge of the circular flat surface of the PDMS cylindrical substrate with a contact angle of θp (Figure 1A) at the edge. Meanwhile, the interfacial tension retracted the liquid polymer to the center from the pinning edge, resulting in the formation of a curvature.36-37 In addition, the liquid polymer can be held on to the PDMS substrate if the value of θp is less than or equal to the critical contact angle for spreading over the edge (θc), which is explained by Gibbs inequality condition, as follows:33-35 𝜃c = (180 − ∅) + 𝜃𝑒 ,

(1)

where ∅ and θe are subtended angles at the edge and the equilibrium (thermodynamic) contact angle, respectively (Figure 1A). According to the Gibbs inequality condition, the calculated value of θc in our system was equal to 140° (∅ and θe in our experiment were 90°and 50°, respectively). This means that θp can be manipulated up to 140° by adjusting the volume of the dropped liquid polymer. To obtain the value of θp equal to 90°, we optimized the amount of the liquid polymer on each PDMS substrate in a reproducible and controllable manner, which resulted in the value of θp , 90°± 0.5°. Figure 1B-F show the sessile droplets of liquid NOA 61 on PDMS substrates with


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different diameters. It was found that the sessile droplets with perfect hemispherical shapes were created on the 2.5- and 3-mm PDMS substrates (Figure 1B and 1C). However, when the diameter of the circular PDMS substrate was increased to 4, 5, and 6 mm, the deformation of the sessile droplet geometry was observed (Figure 1D–1F). In addition, the droplet profile was affected by gravity and interfacial tension.38-41 Compared with the effect of interfacial tension, the effect of gravity force is diminished or is negligible if the droplet size is adequately small.38-39 However, as we increased the size of sessile droplets, the effect of gravity force increased, which is the primary reason for the deformation of sessile droplet geometry in our case. In the previous section, we demonstrated the formation of sessile droplets of NOA 61 on PDMS cylindrical substrates. Hemispherical prisms were formed after the sessile droplets were cured under UV light. Our method could create an optically smooth surface without additional surface polishing because of interfacial tension of liquid. An appropriate surface polishing process is an essential step in minimizing surface roughness in the conventional procedure used for fabricating glass prisms to fulfill the requirement of precision optics42-44, because a high degree of surface roughness causes scattering of incident light and reduces the quality of optics.30, 45 As shown in Figure 2A, a high clarity prism could be observed by naked eyes. AFM characterization was conducted to reveal the surface morphology of the prism. The result clearly showed that the surface morphology of the convex side of the prism was optically smooth with a root-mean-square surface roughness (Rrms) of 0.35 nm (Figure 2C), because the liquid droplet had an appreciable smooth surface.40, 46 Thus, optics with an exceptional smooth surface could be formed after curing. Meanwhile, the AFM inspection shows that the surface morphology of the planar side of the prism was also significantly smooth with an Rrms value of 0.65 nm (Figure 2D), which is much smaller than that of a glass slide (Rrms = 2.13 nm, Figure S3A). This is because the formation of sessile


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droplets was performed on circular flat PDMS cylindrical substrates with considerably smooth surface roughness (Rrms = 0.44 nm, Figure S3B). The results reveal the possibility of using the fabricated prisms as high-quality optics with low light scattering. Hence, the significant light transmission property in the VIS-NIR region of NOA 61 enabled its use without any interference, as shown in Figure S4. The fabricated prisms were used as miniature SPR sensor chips to demonstrate their versatility in sensitive optical-based sensing applications. In the case of thin metal films, such as gold and silver films, SPR is surface plasmon polaritons (SPPs) propagated along dielectric/metal interface.30, 47 We easily produced SPR sensor chips based on Kretschmann configuration by the deposition of 3-nm Cr and 47-nm gold film on the planar side of the prism (Figure 2B). Figure S5 shows digital photographs of the developed SPR sensor chip (A), conventional SPR sensor chips made of S-LAH 60 (B) glass substrates and right-angle prisms (C). The photograph clearly reveals that the developed SPR sensor chip is markedly smaller in size and ready to be used to couple the incident light into SPR. This allowed the use of miniature SPR sensor chips in portable SPR systems without any requirement of additional optical prisms and immersion oil. Compared to the price of traditional SPR sensor chip (Table S1), the production cost for our SPR sensor chips is lower (estimated cost is approximately US$ 2 per piece for a batch of 50 pieces, see Table S2 for the detail of estimation cost), so that the development of disposable SPR sensor chips is possible. The wavelength-modulated SPR technique exhibits a high ability to be miniaturized, which is different from that of angular-modulation-based SPR. In addition, the miniaturization of angularmodulated SPR system is complicated by the requirement of appropriate position of the positionsensitive photosensor.21 To investigate the performance of developed SPR sensor chips, wavelength-modulated SPR characterization was conducted. The fabricated SPR sensor chips


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were then mounted on 3D-printed holders for easy handling (Figure S6). Figure 3A shows the schematic of the SPR excitation that was characterized in air (n = 1.00028) under illumination of polarized light. Figures 3B–3F show SPR reflectivity curves obtained from SPR sensor chips with different diameters. The results clearly show that the developed sensor chips coupled the incident light into SPR. The blue shift of the SPR excitation wavelength was observed as the incident angle increased. We found that a higher incident angle was necessary to couple the incident light into SPR in the modulated wavelength region when the size of SPR chips was increased. Moreover, the excitation angle of the same resonance wavelength also increased by increasing the sensor chip diameter. In principle, the shift of SPR resonance wavelength occurs with the change of incident angle and/or reflective index of dielectric media.23, 25, 48 Because all fabricated SPR sensor chips were made of the same material (cured NOA 61, n= 1.560) and the SPR reflectivity curves were measured in the same environment, the reasonable explanation for the change of excitation angles found in this system is related to the deformation of prism geometry, as seen in Figure 1. A miniature SPR analysis module was developed. A 6-mm SPR sensor chip was fixed on a 3D-printed flow cell to become a disposable microfluidic SPR system (Figure 4A and 4B). This disposable microfluidic SPR system was designed for small-scale SPR analysis with the cell volume of ~280 µL. When water (n = 1.333) was injected into the cell, the resonance angle increased because of the increase of reflective index in comparison with air environment. The blue shift of SPR dips was also observed as the incident angle was increased (Figure S7). The reflective index sensitivity of the fabricated microfluidic SPR system was evaluated based on wavelengthmodulated SPR measurements. The incident angle was fixed at 82°, at which the resonance wavelength was observed at 603 nm. We found that the resonance angle is a little high for the


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refractive index of 1.560 prism. This is because of the refraction of incident light at the air/prism interface because the NOA 61 prism was slightly deformed due to the gravity as observed in Figure 1. The aqueous solutions of ethylene glycol (EG) (n = 1.333–1.383) were injected into the cells.49 Because the reflective index of water/EG solution depends on the concentration of EG, the SPR dips gradually red shifted from 603 to 669 nm on increasing the EG concentration. The result reveals that the reflective index sensitivity of the miniature SPR sensor chip was 1315.2 nm RIU 1

, which is comparable with that of convectional SPR sensor chips (Figure S8). We investigated the applications of the miniature microfluidic SPR system. First, to study the

detection capability of nanometer-sized materials, the device was used to monitor the formation of PDADMAC/PSS LbL ultrathin films. The formation of PDADMAC/PSS LbL ultrathin films was also characterized by traditional SPR setup for the comparison (Figure S9). Figures 5A and 5B show the structure of PDADMAC/PSS LbL ultrathin films on the surface of the sensor chips and the SPR reflectivity curves of PDADMAC/PSS bilayers with various numbers of bilayers. The results clearly show the red shift of the SPR dip as the number of bilayers increased. The relationship of wavelength shifts and the number on bilayers presents good linearity, as shown in Figure 5C. Compared to those of traditional SPR, this result clearly indicates that the developed microfluidic SPR sensor system can be applicable for the detection of nanometer-sized materials. The miniature microfluidic SPR system was also used as an immunosensor for the detection of human IgG. To fabricate the immunosensor, self-assembled monolayer (SAM) of 11-MUA was first deposited on the surface of SPR chips. EDC/NSH was introduced for the activation by forming the hydroxysuccinimide ester before performing an immunoassay, as schematically shown in Figure S10A.7, 50-52 Binding molecules on the surface of SPR chips caused the change of reflective index and could be used for the real-time monitoring, as shown in Figure S10. As a result, we


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clearly revealed that the developed microfluidic SPR module could be used as SPR sensors. This confirms that SPR sensors can not only be fabricated from polymers but 9 can also be used for real-time applications. The use of a 3D printer for the fabrication of a sensor module enables the wide range adaptation as simple detection systems.

4. CONCLUSIONS We developed the miniature SPR sensor chips using confined sessile drop technique. By using edge effect in wetting, the sharp edges of PDMS substrates prevented the overflow of liquid NOA 61 at the edge of substrates, facilitating the formation of sessile droplets. The formation of hemispherical polymeric prisms on PDMS substrates could be achieved after UV curing. The fabricated prisms exhibited highly smooth surfaces that match the quality of precision optics both on convex and planar sides without additional complicated surface polishing. The polymeric prisms were then used to fabricate miniature SPR sensor chips. The miniature SPR sensor chips provided a comparable sensitivity to conventional SPR chips. By applying the miniature SPR sensor chip to 3D-print flow cell, we demonstrated the potential application of a microfluidic SPR analytical module as an immunosensor. The development of the miniature sensor chips has been accomplished by minimizing the production cost. It could be beneficial and fulfill the demand for the cost-effective sensing applications.


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B

A

NOA 61

NOA 61

PDMS θc

θe

θp

PDMS

C

D

E

F

Figure 1. (A) Schematic diagram of the formation of a sessile droplet on the circular flat surface of the PDMS cylindrical substrate. Photographic images of NOA 61 sessile droplets on circular flat surfaces of PDMS cylindrical substrates having different diameters of (B) 2.5, (C) 3, (D) 4, (E) 5 and (F) 6 mm. The photographic images were taken 24 h after the formation of the sessile droplets. Scale bars indicate 1 mm


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Figure 2. Digital photographs of (A) a 6-mm (diameter) polymeric prism after peeling off the PDMS cylindrical substrate and (B) a 6-mm miniature SPR chip. AFM images illustrate the surface morphology (5 m × 5 m) of the 6-mm (diameter) polymeric prism on (C) convex and (D) planar sides, respectively.


15


Cr

B: Dia. 2.5 mm

Air Au

Reflectivity (p/s)

A

NOA 61

p-pol

θi θr

1.00 0.75 40 41 42 43

0.50 0.25

Light source

Detector

Reflectivity (p/s)

Reflectivity (p/s)

1.00

0.75

0.25

0.75

40 41 42 43

44 45 46 47

48 49 50 51

0.25

49 50 51 52

53 54 55 56

450 500 550 600 650 700 750 800 Wavelength (nm)

E: Dia. 5 mm Reflectivity (p/s)

F: Dia. 6 mm

1.00

1.00

0.75

0.25

45 46 47 48

0.50

450 500 550 600 650 700 750 800 Wavelength (nm)

0.50

48 49 50 51

D: Dia. 4 mm

1.00

0.50

44 45 46 47

450 500 550 600 650 700 750 800 Wavelength (nm)

C: Dia. 3 mm

Reflectivity (p/s)

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

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0.75

49 50 51 52

53 54 55 56

57 58 59 60

450 500 550 600 650 700 750 800 Wavelength (nm)

0.50 0.25

51 52 53 54

55 56 57 58

59 60 61 62

450 500 550 600 650 700 750 800 Wavelength (nm)

Figure 3. (A) Schematic illustration of the surface plasmon excitation using SPR sensor chip. SPR reflectivity curves in air of SPR sensor chip with different diameters at (B) 2.5, (C) 3, (D) 4, (E) 5 and (F) 6 mm. The insert pictures in (B)-(F) illustrated the shape of SPR sensor chip.


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A

Syringe needle

Hole

B

Hole

Inlet

Outlet

Miniature SPR sensor chip

Flow cell

Flow channel

SPR sensor chip mounting socket

1.0

Reflectivity (p/s)

C 0.8

0.6

0 % w/w 10 % w/w 20 % w/w 30 % w/w 40 % w/w 50 % w/w

0.4

500

550

600 650 700 Wavelength (nm)

750

EG EG EG EG EG EG

800

80

D Wavelength shift (nm)

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


60

40

20

0 1.33

R2 = 0.9936 Slope = 1,315.2 1.34

1.35 1.36 1.37 Reflective index

1.38

1.39

Figure 4. (A) The complete design of a miniature surface plasmon sensor chip attached to 3Dprinted microfluidic flow cell. (B) Schematic illustrates the internal flow channel of the microfluidic flow cell. (C) SPR reflectivity curves obtained form EG-water solution (0 – 50 % w/w, n = 1.333–1.383 ).49 (D) Reflexive index sensitivity of the developed miniature microfluidic SPR system.


17


A PSS

- - - - - + - +- +- +- + +- +- +- +- +-+ -+ -+ -+ -+ + - + -+ -+ -+

PDADMAC

2bilayers PDADMAC/PSS

Au Cr NOA 61 MPS

Reflectivity (p/s)

0.8

B

0.6

0.4 Au Au/3MPS Au/3MPS/2LBL Au/3MPS/4LBL Au/3MPS/6LBL Au/3MPS/8LBL Au/3MPS/10LBL

0.2

0.0 500 550 600 650 700 750 800 850 900 Wavelength (nm) 180

Wavelength shift (nm)

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

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160

C

140 120

100 80

R2 = 0.9679 Slope = 12.7

60 40

2

4

6

8

10

Number of PDADMAC/PSS bilayers

Figure 5. (A) Schematic illustration of the structure of PDADMAC/PSS bilayers on the surface of the miniature SPR sensor chip. (B) SPR reflectivity curves (p/s) of PDADMAC/PSS bilayers in water from 2 to 10 bilayers. (C) the plot of the number of PDADMAC/PSS bilayers and the wavelength shift.


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ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Fabrication processes of miniature surface plasmon sensor chip. Digital photographs of NOA 61 droplets on flat PDMS sheet. AFM images of PDMS substrates. Transmission spectra of a glass slide and the NOA 61-coated glass slide. Digital photographs of SPR sensor chips and prisms. Photographs of the fabricated miniature NOA 61 SPR sensor chips. SPR reflectivity curves (p/s) of miniature SPR sensor chips and conventional SPR sensor chips. The SPR-binding curve indicates the molecular adsorption on the surfaces of miniature microfluidic SPR sensor chip.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (A. B.) Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Sources Japan Society for the Promotion of Science (JSPS): JP17F17361 Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS


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This work was supported by a Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Number JP17F17361. S.N. gratefully thanks the JSPS for Postdoctoral Fellowship. S.N. would like to thank the Development and Promotion of Science and Technology Talents Project (DPST), Thailand. S.E. and W.J. acknowledge financial support from the Ratchadaphiseksomphot Endowment Fund, Chulalongkorn University (Sci-Super III - 004).

REFERENCES 1. 2.

3.

4. 5.

6. 7.

8. 9. 10.

Bakhtiar, R., Surface Plasmon Resonance Spectroscopy: A Versatile Technique in a Biochemist’s Toolbox. J. Chem. Educ. 2013, 90 (2), 203-209. Rebois, R. V.; Schuck, P.; Northup, J. K., [2] - Elucidating Kinetic and Thermodynamic Constants for Interaction of G Protein Subunits and Receptors by Surface Plasmon Resonance Spectroscopy. In Methods in Enzymology, Iyengar, R.; Hildebrandt, J. D., Eds. Academic Press: San Diego, 2002; Vol. 344, pp 15-42. Schmidt, A.; Utepbergenov, D. I.; Krause, G.; Blasig, I. E., 2 - Direct Demonstration of Association of the Blood-Brain Barrier Proteins ZO-1 and Occludin Using Surface Plasmon Resonance Spectroscopy; Effect of SIN-1. In Blood-Spinal Cord and Brain Barriers in Health and Disease, Sharma, H. S.; Westman, J., Eds. Academic Press: San Diego, 2004; pp 11-17. Drescher, D. G.; Selvakumar, D.; Drescher, M. J., Chapter One - Analysis of Protein Interactions by Surface Plasmon Resonance. In Advances in Protein Chemistry and Structural Biology, Donev, R., Ed. Academic Press: San Diego, 2018; Vol. 110, pp 1-30. Moran, K. L. M.; Lemass, D.; O'Kennedy, R., Chapter 6 - Surface Plasmon Resonance– Based Immunoassays: Approaches, Performance, and Applications. In Handbook of Immunoassay Technologies, Vashist, S. K.; Luong, J. H. T., Eds. Academic Press: San Diego, 2018; pp 129-156. Tangkawsakul, W.; Srikhirin, T.; Shinbo, K.; Kato, K.; Kaneko, F.; Baba, A., Application of Long-Range Surface Plasmon Resonance for ABO Blood Typing. Int. J. Anal. Chem. 2016, 2016, Article ID 1432781. Janmanee, R.; Baba, A.; Phanichphant, S.; Sriwichai, S.; Shinbo, K.; Kato, K.; Kaneko, F., In Situ Electrochemical-Transmission Surface Plasmon Resonance Spectroscopy for Poly(pyrrole-3-carboxylic acid) Thin-Film-Based Biosensor Applications. ACS Appl. Mater. Interfaces 2012, 4 (8), 4270-4275. Salamon, Z.; Macleod, H. A.; Tollin, G., Coupled Plasmon-Waveguide Resonators: A New Spectroscopic Tool for Probing Proteolipid Film Structure and Properties. Biophys. J. 1997, 73 (5), 2791-2797. Tang, Y.; Zeng, X.; Liang, J., Surface Plasmon Resonance: An Introduction to a Surface Spectroscopy Technique. J. Chem. Educ. 2010, 87 (7), 742-746. Karlsson, R.; Michaelsson, A.; Mattsson, L., Kinetic Analysis of Monoclonal Antibody-


20

Page 21 of 23 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


11.

12. 13. 14. 15. 16. 17. 18.

19. 20. 21. 22. 23. 24. 25.

Antigen Interactions with a New Biosensor Based Analytical System. J. Immunol. Methods 1991, 145 (1), 229-240. Gobi, K. V.; Kim, S. J.; Tanaka, H.; Shoyama, Y.; Miura, N., Novel Surface Plasmon Resonance (SPR) Immunosensor Based on Monomolecular Layer of Physically-Adsorbed Ovalbumin Conjugate for Detection of 2,4-Dichlorophenoxyacetic Acid and Atomic Force Microscopy Study. Sens. Actuator B-Chem. 2007, 123 (1), 583-593. Wang, S.; Zhao, S.; Wei, X.; Zhang, S.; Liu, J.; Dong, Y., An Improved Label-Free Indirect Competitive SPR Immunosensor and Its Comparison with Conventional ELISA for Ractopamine Detection in Swine Urine. Sensors (Basel) 2017, 17 (3), 604. Makaraviciute, A.; Ramanavicius, A.; Ramanaviciene, A., Development of a Reusable Protein G Based SPR Immunosensor for Direct Human Growth Hormone Detection in Real Samples. Anal. Methods 2015, 7 (23), 9875-9884. Wolf, L. K.; Gao, Y.; Georgiadis, R. M., Kinetic Discrimination of Sequence-Specific DNA−Drug Binding Measured by Surface Plasmon Resonance Imaging and Comparison to Solution-Phase Measurements. J. Am. Chem. Soc. 2007, 129 (34), 10503-10511. Hendrix, M.; Priestley, E. S.; Joyce, G. F.; Wong, C.-H., Direct Observation of Aminoglycoside−RNA Interactions by Surface Plasmon Resonance. J. Am. Chem. Soc. 1997, 119 (16), 3641-3648. Preechaburana, P.; Gonzalez, M. C.; Suska, A.; Filippini, D., Surface Plasmon Resonance Chemical Sensing on Cell Phones. Angew. Chem. Int. Edit. 2012, 51 (46), 11585-11588. Liu, Y.; Liu, Q.; Chen, S.; Cheng, F.; Wang, H.; Peng, W., Surface Plasmon Resonance Biosensor Based on Smart Phone Platforms. Sci. Rep. 2015, 5, 12864. Filho, C. A. d. S.; Lima, A. M. N.; Neff, H. In Smartphone Based, Portable Optical Biosensor Utilizing Surface Plasmon Resonance, 2014 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) Proceedings, Montevideo, Uruguay, May 12-15, 2014; IEEE Roda, A.; Michelini, E.; Zangheri, M.; Di Fusco, M.; Calabria, D.; Simoni, P., SmartphoneBased Biosensors: A Critical Review and Perspectives. Trends Anal. Chem. 2016, 79, 317325. Janmanee, R.; Chuekachang, S.; Sriwichai, S.; Baba, A.; Phanichphant, S., Functional Conducting Polymers in the Application of SPR Biosensors. J. Nanotec. 2012, 2012, Article ID 620309. Homola, J.; Dostálek, J.; Chen, S.; Rasooly, A.; Jiang, S.; Yee, S. S., Spectral Surface Plasmon Resonance Biosensor for Detection of Staphylococcal Enterotoxin B in Milk. Int. J. Food Microbiol. 2002, 75 (1), 61-69. Shankaran, D. R.; Gobi, K. V.; Miura, N., Recent Advancements in Surface Plasmon Resonance Immunosensors for Detection of Small Molecules of Biomedical, Food and Environmental Interest. Sens. Actuator B-Chem. 2007, 121 (1), 158-177. Homola, J.; Koudela, I.; Yee, S. S., Surface Plasmon Resonance Sensors Based on Diffraction Gratings and Prism Couplers: Sensitivity Comparison. Sens. Actuator B-Chem. 1999, 54 (1–2), 16-24. Homola, J.; Yee, S. S.; Gauglitz, G., Surface Plasmon Resonance Sensors: Review. Sens. Actuator B-Chem. 1999, 54 (1–2), 3-15. Homola, J.; Piliarik, M., Surface Plasmon Resonance (SPR) Sensors. In Surface Plasmon Resonance Based Sensors, Homola, J., Ed. Springer Berlin Heidelberg: Berlin, Heidelberg, 2006; pp 45-67.


21


26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44.

Page 22 of 23

Yeatman, E. M., Resolution and Sensitivity in Surface Plasmon Microscopy and Sensing. Biosens. Bioelectron. 1996, 11 (6), 635-649. Laksono, F. D.; Supardianningsih; Arifin, M.; Abraha, K., Development of Low Cost and Accurate Homemade Sensor System Based on Surface Plasmon Resonance (SPR). J. Phys. Conf. Ser 2018, 1011 (1), 012043. Chen, R.; Wang, M.; Wang, S.; Liang, H.; Hu, X.; Sun, X.; Zhu, J.; Ma, L.; Jiang, M.; Hu, J.; Li, J., A Low Cost Surface Plasmon Resonance Biosensor Using a Laser Line Generator. Opt. Commun. 2015, 349, 83-88. Lan, G.; Liu, S.; Zhang, X.; Wang, Y.; Song, Y., A Simplified High Figure-of-Merit PrismFree Surface Plasmon Resonance Refractive Index Sensor Based on Self Adaptive Angular Interrogation. Rev. Sci. Instrum. 2015, 86 (2), 025006. Hinman, S. S.; McKeating, K. S.; Cheng, Q., Plasmonic Sensing with 3D Printed Optics. Anal. Chem. 2017, 89 (23), 12626-12630. Zhang, L. L.; Chen, X.; Sun, J. H.; Cai, H. Y.; Li, H.; Chao, Y. P.; Cui, D. F., A Poly(dimethylsiloxane) Based Prism for Surface Plasmon Resonance Imaging System and Its Application for Gas Detection. Rev. Sci. Instrum. 2013, 84 (3), 035001. Geng, Z.; Li, Q.; Wang, W.; Li, Z., PDMS Prism-Glass Optical Coupling for Surface Plasmon Resonance Sensors Based on MEMS Technology. Sci. China Inf. Sci. 2010, 53 (10), 2144-2158. Ekgasit, S.; Kaewmanee, N.; Jangtawee, P.; Thammacharoen, C.; Donphoongpri, M., Elastomeric PDMS Planoconvex Lenses Fabricated by a Confined Sessile Drop Technique. ACS Appl. Mater. Interfaces 2016, 8 (31), 20474-20482. Fang, G.; Amirfazli, A., Understanding the Edge Effect in Wetting: A Thermodynamic Approach. Langmuir 2012, 28 (25), 9421-9430. Bayramli, E.; Mason, S. G., Liquid Spreading: Edge Effect for Zero Contact Angle. J. Colloid Interface Sci. 1978, 66 (1), 200-202. Bergeron, V.; Bonn, D.; Martin, J. Y.; Vovelle, L., Controlling Droplet Deposition with Polymer Additives. Nature 2000, 405, 772-775. Sugiura, S.; Nakajima, M.; Iwamoto, S.; Seki, M., Interfacial Tension Driven Monodispersed Droplet Formation from Microfabricated Channel Array. Langmuir 2001, 17 (18), 5562-5566. Vafaei, S.; Podowski, M. Z., Analysis of the Relationship Between Liquid Droplet Size and Contact Angle. Adv. Colloid Interface Sci. 2005, 113 (2), 133-146. Vafaei, S.; Podowski, M. Z., Theoretical Analysis on the Effect of Liquid Droplet Geometry on Contact Angle. Nucl. Eng. Des. 2005, 235 (10), 1293-1301. Ren, H.; Xu, S.; Wu, S.-T., Effects of Gravity on the Shape of Liquid Droplets. Opt. Commun. 2010, 283 (17), 3255-3258. Roy, A. C.; Yadav, M.; Arul, E. P.; Khanna, A.; Ghatak, A., Generation of Aspherical Optical Lenses via Arrested Spreading and Pinching of a Cross-Linkable Liquid. Langmuir 2016, 32 (21), 5356-5364. Onwuka, G.; Abou-El-Hossein, K., Surface Roughness in Ultra-High Precision Grinding of BK7. Proc. Cirp. 2016, 45, 143-146. Ghosh, G.; Sidpara, A.; Bandyopadhyay, P. P., Fabrication of Optical Components by Ultraprecision Finishing Processes. In Micro and Precision Manufacturing, Gupta, K., Ed. Springer International Publishing: Cham, 2018; pp 87-119. Tsai, K.-M.; Hsieh, C.-Y.; Lo, W.-C., A Study of the Effects of Process Parameters for


22

Page 23 of 23 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


45. 46. 47. 48.

49. 50. 51. 52.

Injection Molding on Surface Quality of Optical Lenses. J. Mater. Process. Technol. 2009, 209 (7), 3469-3477. Trost, M.; Schröder, S., Roughness and Scatter in Optical Coatings. In Optical Characterization of Thin Solid Films, Stenzel, O.; Ohlídal, M., Eds. Springer International Publishing: Cham, 2018; pp 377-405. Kamal, T.; Watkins, R.; Cen, Z.; Rubinstein, J.; Kong, G.; Lee, W. M., Design and Fabrication of a Passive Droplet Dispenser for Portable High Resolution Imaging System. Sci. Rep. 2017, 7, 41482. Li, M.; Cushing, S. K.; Wu, N., Plasmon-Enhanced Optical Sensors: A Review. Analyst 2015, 140 (2), 386-406. Takagi, K.; Nair, S. V.; Watanabe, R.; Seto, K.; Kobayashi, T.; Tokunaga, E., Surface Plasmon Polariton Resonance of Gold, Silver, and Copper Studied in the Kretschmann Geometry: Dependence on Wavelength, Angle of Incidence, and Film Thickness. J. Phys. Soc. Jpn. 2017, 86 (12), 124721. Fogg, E. T.; Hixson, A. N.; Thompson, A. R., Densities and Refractive Indexes for Ethylene Glycol-Water Solutions. Anal. Chem. 1955, 27 (10), 1609-1611. Liang, K.; Wu, H.; Li, Y., Immune-Enrichment of Insulin in Bio-Fluids on GoldNanoparticle Decorated Target Plate and In Situ Detection by MALDI MS. Clin. Proteom. 2017, 14 (1), 5. Kamra, T.; Chaudhary, S.; Xu, C.; Montelius, L.; Schnadt, J.; Ye, L., Covalent Immobilization of Molecularly Imprinted Polymer Nanoparticles on A Gold Surface Using Carbodiimide Coupling for Chemical Sensing. J. Colloid Interface Sci. 2016, 461, 1-8. Ahmad, A.; Moore, E., Electrochemical Immunosensor Modified with Self-Assembled Monolayer of 11-Mercaptoundecanoic Acid on Gold Electrodes for Detection of Benzo[a]pyrene in Water. Analyst 2012, 137 (24), 5839-5844.

BRIEF. Photographs of NOA 61 hemispherical prism, the design of SPR flow cell, and 3D printed SPR flow cell coupled with NOA61 surface plasmon sensor chip. SYNOPSIS TOC Syringe needle

Hole

Hole

Inlet

Outlet

Miniature SPR sensor chip Flow cell

Flow channel

SPR sensor chip mounting socket


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Fabrication of Miniature Surface Plasmon Resonance Sensor Chips

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