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We present a polymer-coated silicon microring resonator to detect volatile organic compounds (VOC) gases. Absorption of VOC gases into the polymer alters the refractive index around the microring, which enables quantification of absorbed gases as a resonance wavelength shift in the resonator. Two different polymers, hyperbranched polyesteramid and poly(2-vinyl pyridine), are tested as the absorption layers on the highly sensitive (80 nm/RIU and 10,000 Q-factor) silicon microring resonator. The sensing responses to VOC gases are characterized by flowing four different gases: styrene, acetone, toluene, and isoprene, in a wide range of concentration (sub-ppm to 100 ppm range). The hyperbranched polyesteramid coated sensor shows the highest sensitivity to styrene. Similarly, Poly(2-vinyl pyridine) coated device exhibits sensitive responses to styrene and acetone. From experiments with a wide range of gas concentrations, we observe that the sensors have two distinguished characteristics; linear and non-linear response with respect to gas concentration. To account for it, a dual mode sensing mechanism is proposed; Langmuir mode (doping effect) in the low concentration (

MicroRNAs have been identified as promising biomarkers for human diseases. The development of a point-of-care (POC) test for the disease-associated miRNAs would be especially beneficial, since miRNAs are unexpectedly well preserved in various human specimens, including urine. Here, we present the Mach-Zehnder interferometer-miRNA detection system capable of detecting multiple miRNAs in clinical urine samples rapidly and simultaneously in a label-free and real-time manner. Through measurement of the light phase change, the MZI sensor provides an optical platform for fast profiling of small molecules with improved accuracy. We demonstrate that this system could specifically detect target miRNAs (miR-21, and let-7a), and even identify the single nucleotide polymorphism of the let-7 family of miRNAs from synthetic and cell line samples. The clinical applicability of this system is confirmed by simultaneously detecting two types of miRNAs in urine samples of bladder cancer patients in a single reaction, with a detection time of 15 min. The POC system can be expanded to detect a number of miRNAs of different species and should be useful for a variety of clinical applications requiring at or near the site of patient care.

We demonstrate a highly sensitive label-free Mach–Zehnder interferometer (MZI) biosensor based on silicon nitride slot waveguide. Unlike the conventional MZI sensors, the sensing arm of the sensor consists of a slot waveguide while the reference arm consists of a strip waveguide. Thanks to the slot waveguide's property to provide high optical intensity in a subwavelength-size low refractive index region (slot region), which allows high light–analyte interaction, higher sensitivity can be obtained as compared to conventional waveguides using the slot waveguide as sensing region. The bulk refractive index sensitivity of the slot waveguide MZI sensor was found to be 1864π/RIU (refractive index unit) with 7 mm long slot waveguide sensing arm, which shows higher sensitivity compared to the conventional MZI device based on silicon nitride. The biosensing capability of the developed slot waveguide MZI was investigated using biotin–streptavidin binding as a model system. The sensitivity of the system was demonstrated down to 18.9 fM or 1 pg/ml of streptavidin solution and to the best of our knowledge, it is the best reported experimental value for the limit of detection of a MZI sensor. Furthermore, we investigated the specific detection and quantification of the methylation of DAPK (Death-associated protein kinase) gene, which is a widely used biomarker for human cancers. We have shown that methylation sequences of DAPK gene of various methylation densities (100%, 50%, and 0% of methylation sites) can be quantified and discriminated even at a concentration as low as 1 fmol/μl or 1 nM. ASTAR (Agency for Sci., Tech. and Research, S’pore)

We present a novel biosensor based on an electrical tracing-assisted silicon dual-microring resonator sensor system. The dual-microring system comprises one microring resonator as a sensing element and the other microring resonator integrated with an electrical controller as a tracing element. The resonance wavelength shift of the sensing microring induced by the refractive index change due to antigen-ligand bindings is traced and determined by direct voltage applied to the electrical tunable tracing microring. The sensor system enables the use of a low-cost broadband light source instead of a bulky and expensive tunable laser, which allows the development of cost-effective point-of-care diagnostic devices by significantly reducing the device cost and increasing its portability. The sensing capability of the developed dual-microring sensor was investigated using biotin-streptavidin binding as a model system. We have demonstrated the quantitative detection of streptavidin over a broad range of concentrations down to 190 pM by monitoring the electrical power applied to the tracing ring. We have also validated the sensing principle of the dual-microring system by a direct comparison between the calculated and measured values for the resonance wavelength shift of the sensing microring. Furthermore, we have shown the quantitative and specific detection of a well-known breast cancer biomarker, human epidermal growth factor receptor 2 (HER2), in a bovine serum albumin solution using the antibody-modified dual-microring sensor system.

We propose an anti-symmetric grating structure for effective excitation of the short-range surface plasmon polariton (SR-SPP) mode of a metal stripe waveguide. The structure consists of two corrugated Bragg gratings offset by half of a period formed on the two sides of the metal stripe, respectively. The SR-SPP mode is excited in the backward direction by the long-range surface plasmon polariton mode launched into the waveguide. We investigate the effects of the metal stripe thickness, the grating corrugation depth, and the number of grating periods on the transmission and reflection characteristics of the grating with the finite-difference time-domain method in detail. Our numerical results show that a peak reflection of ~57% in the SR-SPP mode can be achieved with a 50-μm long grating on a 40-nm thick gold stripe.

Detection and quantification of DNA methylation is important to provide an opportunity to resolve clinical issues such as cancer early detection, progression, and drug treatments. In spite of myriad current technologies for DNA methylation detection that have been developed in last decade, they are still complicated and inadequate to be used as in vitro clinical diagnostic device. This work presents the first methylation specific sensor based on the silicon microring resonators which achieves fast, simple and specific label-free detection of DNA methylation after the bisulfite conversion. The methylated promoter regions of three genes ( DAPK , E - cadherin and RARβ ), which have been widely studied as biomarkers for human cancers including bladder cancer, are used as the target DNA sequences. We show that the methylated targets are strongly captured by methylated probe compared to unmethylated probe or vice versa. The discrimination between methylated and unmethylated DNA sequences is achieved within 5 min after hybridization between target and probe. Additionally, we have quantified DNA methylation density using various proportions (100, 75, 50, 25, and 0% of methylation sites) of methylation sequences of DAPK gene. Finally, we confirmed that the sensor can clearly detect the methylation of RARβ gene by using amplified target from genomic DNA of cancer cells. Therefore, our technique can be used to detect and quantify the methylation density in cancer biomarkers.

This paper reports on the design and fabrication of Poly(dimethylsiloxane) (PDMS) single mode rib waveguide. PDMS was chosen as the base material for both the core and cladding of the waveguide. Such a PDMS waveguide allows an easy integration with microoptical components for lab-on-a-chip systems fabricated by soft lithography fabrication methods. The modification of the PDMS refractive index was achieved by diluting the base material with hexane. The fabricated PDMS rib waveguides were characterized for mode profile characteristics and the results confirmed the excitation of the waveguide's fundamental mode. The propagation loss was characterized at a wavelength of 635 nm and found to be 0.48 dB/cm. Such a low loss waveguide is useful as basic building block for complex microphonotnics device.

A monolithic integration of poly(dimethylsiloxane) (PDMS) waveguides and microfluidics is demonstrated by implementing a two-step lithographic moulding. Silicone oil is added in PDMS precursor to tune the refractive index of waveguides with air as the side and top cladding layer. Curved and straight waveguides are characterized for their insertion loss mainly due to propagation, radiation, and transition. Transition and radiation losses are identified dominating along the curves whereas propagation loss increases at a steady rate of 0.249 ± 0.015 dB/cm. With the integrated system, real-time absorbance measurement of fluorescein streams yields a nearly linear response up to 250 μM and the limit of detection

We demonstrate an array of poly(dimethylsiloxane) (PDMS) nano-hemisphere for color separation by using soft lithography techniques. Each array of a PDMS nano-hemisphere has an area of 1080 μm × 820 μm with well-defined period and diameter. The diameter of each nano-hemisphere and period between nano-hemispheres can be varied to produce the desired color. The periods and diameters are (1400, 1120), (1500, 1040), and (1600, 960) nm for red, yellow, and green colors, respectively. The reflection spectrum obtained from coupling between an incident light and the nano-hemispheres array can be utilized for fluorescence spectroscopy as filters or spectral analysis for lab-on-a-chip devices.

This letter presents a novel complementary metal-oxide-semiconductor (CMOS)-compatible technique to fabricate a sub-100-nm slot waveguide in wafer-scale, which is beyond the resolution limit of conventional deep ultraviolet (DUV) lithography. We also demonstrate fabrication of an efficient channel-slot coupler with an ultrasharp tip by using slanted cutting. The propagation loss of the slot wave- guide obtained is ~11.1 ± 1.15 dB/cm for the 100-nm slot and ~8.6 ± 0.61 dB/cm for the 80-nm slot, while each pair of channel-slot couplers has a very low insertion loss of 0.847 ± 0.065 dB. Finally, a Mach-Zehnder interferometer structure-based optical sensor demonstrates the integrate-ability of the proposed circuit.

We proposed and demonstrated label-free optical biochemical sensor realized on a novel bulk silicon-based platform with three-dimensional (3D) monolithic optoelectronic integration circuit (OEIC). The Ge-photodetector (Ge-PD) is integrated on bulk-silicon. Optical functional components are built with CMOS back-end-of-line (BEOL). Via this platform, the label-free optical biochemical sensor can get rid of the expensive SOI wafer. The costly tunable laser-source can be replaced by low cost wide-band light source. Optical signal is converted into electrical signal and read out by on-chip Ge-PD directly. This platform facilitates the development of cost-effective portable point-of-care (POC) diagnostic tool. Meanwhile, this also opens up new ways of electronic and photonic devices monolithically integration in 3D.

In this paper, we study the temperature sensitivity of an electrical tracing-assisted dual-microring optical sensor, which consists of a sensing ring to detect the refractive index change on its surface and a tracing ring to trace the resonance wavelength shift of the sensing ring by the thermo-optic effect with a heating electrode on it. The wavelength shift measurement is therefore changed to electrical power variation measurement. Thanks to the real-time compensation effect of the tracing ring, the temperature dependence of the sensor is found to be intrinsically low. The resonance wavelength temperature sensitivity difference between the two rings is measured to be as low as 10.1 pm/°C, showing that the temperature dependence of the sensor in terms of wavelength per degree is reduced by ~6 times compared to that of a single ring sensor. The temperature sensitivity of the sensor in terms of electrical power per degree is measured to be −0.077 mW/°C. By using tracing ring with enhanced tuning efficiency, this value can be further decreased to −0.0057 W/°C. The experimental results agree well with the expectation. This type of sensors with low temperature dependence has great potential to be deployed in various practical point-of-care diagnostic applications.

Here, we present an integrated Lab-on-a-Chip (LOC) system based on silicon microring resonator devices. The system comprises of an electrical tracing-assisted silicon dual-microring sensor which requires a low-cost broadband light source instead of a bulky and expensive tunable laser therefore allows the development of cost-effective point-of-care (POC) diagnostic device. Highly efficient and fast nucleic acids detection with silicon microring device is demonstrated using an isothermal solid-phase amplification/detection (ISAD) technique. The integrated LOC system consists of dualmicroring sensors and microfluidic device for sample processing together with ISAD technique offers true realization of POC device for human disease diagnosis.

We present a novel label-free bio-photonic sensing system based on silicon opto-electric integrated circuit (OEIC) platform. The sensing system comprises an electrical-tracing assisted microring and a sensor microring integrating with an on-chip photodetector for direct electrical read-out. Multiplexing is achieved through an array of microrings and integrated photodetectors. Such sensing system circumvents the need of an expensive wavelength-tunable laser source by a low-cost broadband light source. This facilitates the development of a cost-effective point-of-care (POC) diagnostic tool. The completed system was demonstrated for label-free and multiplexed detection of DNA targets of pathogenic bacteria.

In this paper, we suggest a simple and inexpensive method for the enhancement of binding performance with low pressure drop using density difference between core fluid and sheath fluid. Simulations and parametric studies of the method have been performed using computational fluid dynamics (CFD) simulation program and the results were validated by fluorescence experiments using fluorescent polystyrene beads and streptavidin labeled with fluorescent dye.

We demonstrate a cost-effective silicon microring-based bio/chemical sensor, which integrates vertical grating couplers, two cascaded microrings for optical sensing and electrical tracing, and Ge photodetector for direct sensing interrogation. Detection limit of 1.5×10-5 is demonstrated.

Bladder cancer is one of the most common cancers in Worldwide. The determination of urinary telomerase activity is a promising tool for the diagnosis of bladder carcinoma owing to the high rate of expression of telomerase in cancer cells. Typical assay for telomerase activity is the telomeric repeat amplification protocol (TRAP) based on polymerase chain reaction (PCR) amplification. However, TRAP assay is susceptible to PCR-derived artifacts and requires time-consuming procedure, expensive equipments and reagents. To develop a new method for telomerase activity assay that is fast, simple, and cost-effective, we have examined a silicon-based microring resonator biosensor to detect label-free, PCR-free telomerase activity using telomerase extracted from two bladder cancer cell lines, J-82 and HT-1376, in a buffer solution and spiked urine. With telomerase primer immobilized microring resonator sensor system, we successfully demonstrate the detection of telomerse extracted from as little as 10 cells/μL and 100 cells/μL in buffer and urine, respectively. Especially, the results represented here is the first demonstration of the detection of telomerase activity in human urine on the chip-based system. From the results, we expect that the silicon photonic microring resonator system can provide a powerful tool for cost-effective and sensitive telomerase activity detection in urinary bladder cancer.

We demonstrate a volatile organic compounds (VOC) gas detection using silicon based microring resonator devices. Polymer is chemically attached to sidewall of silicon waveguide and microring as a cladding layer. Absorption of VOC gases into the polymer film induces a resonance wavelength shift. A detection limit of 10 part per million (ppm) for both toluene and acetone has been achieved.

We propose a new method of exciting short-range surface plasmon polariton (SR-SPP) mode with a long-rang surface plasmon polariton mode, both of which are supported by a thin metal stripe embedded in a dielectric, using a double-sided anti-symmetric grating formed on the metal stripe. The effects of the metal stripe thickness, the grating corrugation depth and the number of grating periods on the transmission and reflection spectra are investigated numerically, and it is verified that light can be efficiently coupled to SR-SPP mode with the grating.

We explore the optical biosensing platform in plasmonic nanoholes array. The periodic nanohole structure of the biosensor and the gold coating of the sensor surface produce extraordinary light transmission (EOT) resonances of which the resonance peak shifts proportionately to the change of environment refractive index (RI). Detailed simulations studies were carried out to establish the resonance spectrum and sensitivity in relationship with the nanohole array pitch, diameter and gold thickness for hexagonal lattice arrangement. The plasmonic sensors were fabricated by top down approach utilizing mask-based deep ultraviolet (DUV) lithography. The plasmonic nanohole sensor was tested with a direct coupling method of incident light which allows robust and sensitive sensing platform with minimal alignment requirements. The measured bulk refractive index sensitivity is 409.4 nm/RIU and the surface mass sensitivity is 1.802 nm/ng mm−2. The sensor structures have shown promising designs and performance for achieving compact and low-cost sensor for biosensing applications.

We propose an efficient multiplexed sensing system for detecting bladder cancer biomarkers without invasiveness, labeling, and high cost using a silicon-based dual microring resonator biosensor. The dual microring biosensor consists of a sensing microring and an electrical tracing microring. The working principle of the sensor is that a resonance wavelength shift of sensing ring is induced by the refractive index change resulted from biomarker binding to the ligand on the sensing microring. Then, the shift is traced and determined by the tracing ring through direct voltage supply. Also, we have shown the specific detection of HER-2 protein which is known as one of bladder cancer biomarker using the dual microring sensor.

We present a label-free aptamer sensor based on an array of silicon micro-ring resonators. An array of sensors consists of three sensor rings and a reference ring was fabricated and its surface sensitivity and the limit of detection was obtained using polyelectrolyte multilayer. The mass sensitivity and the limit of detection of the fabricated sensor ring is 0.35 nm/ng mm−2 and 42.8 pg/mm2 in air and 0.24 nm/ngmm−2 and 62.5 pg/mm2 in water, respectively. We successfully demonstrated the binding assay over a broad range of protein concentrations using a model system with human thrombin as the analyte and DNA aptamers as immobilized ligands.

As the sensitivity and detection limit of photonic refractive index (RI) biosensor increases, the temperature dependence becomes a major challenge. In this paper, we present a Mach-Zehnder Interferometer (MZI) biosensor based on silicon nitride slot waveguides. The biosensor is designed for minimal temperature dependence without compromising the performance in terms of sensitivity and detection limit. With air cladding, the measured surface sensitivity and detection limit of MZI biosensor reach 7.16 nm/(ng mm(-2)) and 1.30 (pg mm(-2)), while achieving a low temperature dependence is 5.0 pm/° C. With water cladding, the measured bulk sensitivity and detection limit reach 1730(2π)/RIU and 1.29 × 10(-5) RIU respectively. By utilizing Vernier effect through cascaded MZI structures, the measured sensitivity enhancement factor is 8.38, which results in a surface detection limit of 0.155 (pg mm(-2)).

We propose and demonstrate a cost effective electrical tracing-assisted silicon microring sensor system which comprises one sensing microring and another thermo-optical-tunable tracing microring. Proof-of-principle demonstation by testing polyelectrolyte multilayer shows the sensitivity of 3.75 mW/ng·mm2.

We have designed, fabricated and characterized poly(dimethylsiloxane) (PDMS) single-mode rib waveguides. PDMS was chosen specifically for the core and cladding. Combined with the soft lithography fabrication techniques, it enables an easy integration of microoptical components for lab-on-a-chip systems. The refractive index contrast, Δ of 0.07% between the core and cladding for single-mode propagation was achieved by modifying the properties of the same base material. Alternatively, a higher refractive index contrast, Δ of 1.18% was shown by using PDMS materials from two different manufacturers. The fabricated rib waveguides were characterized for mode profile characteristics and confirmed the excitation of the fundamental mode of the waveguide. The propagation loss of the single-mode rib waveguide was characterized using the cutback measurement method at a wavelength of 635 nm and found to be 0.48 dB/cm for Δ of 0.07% and 0.20 dB/cm for Δ of 1.18%. Y-branch splitter of PDMS single-mode rib waveguide was further demonstrated.

The monolithic integration of poly(dimethylsiloxane) (PDMS) waveguides with microfluidics is presented. Silicone oil is added in PDMS precursor to tune the refractive index of waveguides with air as the side and top cladding layer. Curved and straight waveguides are characterized for their insertion loss mainly due to propagation, radiation, and transition. For the integrated system, real-time absorbance measurement of fluorescein streams yields a linear response 250 muM and with a limit of detection

In this paper, we demonstrate an optical filter using cladding modulated anti-symmetric long-period grating in a two-mode silicon waveguide. The filter consists of a two-mode waveguide connected with an input and output single-mode waveguide through two linear tapers. The anti-symmetric grating is formed by placing two periodic arrays of silicon squares offset by half of a grating pitch along the two-mode waveguide. Light coupling occurs between two co-propagating modes at the coupling wavelength through the grating and results in a rejection band at the output. The grating pitch, coupling coefficient, transmission spectrum and 3-dB bandwidth of the grating are investigated with the coupled-mode theory. By using a cladding modulated grating, the grating coupling strength can be controlled over a wide range by the two-mode waveguide width or separation distance between the grating and waveguide. Band-rejection filters are experimentally demonstrated in 1-μm, 0.8-μm and 0.7-μm wide two-mode silicon waveguides and rejection bands with different bandwidths and maximal attenuation contrasts larger than 15 dB (~97% coupling efficiency) have been achieved.

We propose and demonstrate a single-channel Mach-Zehnder interferometric (MZI) biochemical sensor consisting of two single-mode waveguides connected by a two-lateral-mode spiral sensing waveguide through two discontinuous junctions. The use of a two-lateral-mode waveguide offers the advantage of simple fabrication using single-step lithography and etching process. Meanwhile, the two-mode waveguide folded in a spiral layout can achieve high sensitivity of a long sensing waveguide while providing a compact sensing area compatible with commercial spotting machine and requiring small volume of sample. The sensor is demonstrated in silicon waveguides and the effect of the discontinuity offset distance on the interference visibility is studied. The bulk and surface sensitivity of a fabricated sensor with a 4582-μm-long two-mode spiral waveguide folded within a 185 μm diameter spot are characterized to be 461.6 π/RIU (refractive index unit) and 1.135 π/ng mm(-2), respectively. The biosensing capability of the sensor is verified by the measurement of biotin-streptavidin interaction of different concentrations.

We demonstrate a silicon-based optoelectronic integrated circuit (OEIC) for label-free bio/chemical sensing application. Such on-chip OEIC sensor system consists of optical grating couplers for vertical light coupling into silicon waveguides, a thermal-tunable microring as a tunable filter, an exposed microring as an optical label-free sensor, and a Ge photodetector for a direct electrical readout. Different from the conventional wavelength-scanning method, we adopt low-cost broadband ASE light source, together with the on-chip tunable filter to generate sliced light source. The effective refractive index change of the sensing microring induced by the sensing target is traced by scanning the supplied electrical power applied onto the tracing microring, and the detected electrical signal is read out by the Ge photodetector. For bulk refractive index sensing, we demonstrate using such OEIC sensing system with a sensitivity of ~15 mW/RIU and a detection limit of 3.9 μ-RIU, while for surface sensing of biotin-streptavidin, we obtain a surface mass sensitivity of Sm = ~192 µW/ng·mm−2 and a surface detection limit of 0.3 pg/mm2. The presented OEIC sensing system is suitable for point-of-care applications. Published version

In this paper, we present a design of a refractive index sensor based on grating-assisted light coupling between a strip waveguide and a slot waveguide. The slot waveguide serves as the sensing waveguide while the strip waveguide is used for light launching and detection. The wavelength at which the light is coupled from the strip waveguide to the slot waveguide serves as a measure of the refractive index of the external medium. The sensitivity of the sensor is ~1.46 × 10(3) nm/RIU (refractive index unit) and can be almost doubled by isolating the strip waveguide from the external medium. The effects of the slot-waveguide parameters on the sensitivity have also been investigated. In particular, it is found that the sensor can achieve extraordinarily high sensitivity (on the order of 10(5) nm/RIU) when the group indices of two waveguides are close. The temperature dependence of the sensor is also investigated and a sensor with very low temperature dependence can be achieved with a polymer isolation layer.

We have designed, fabricated and characterized poly(dimethylsiloxane) (PDMS) arrayed waveguide grating (AWG) with four-channel output for operation in the visible light wavelength range. The PDMS AWG was realized based on the single-mode PDMS rib waveguide. The device was designed for 1 nm channel spacing with the wavelength ranging from 639 to 644 nm. The measured insertion loss is 11.4 dB at the peak transmission spectrum and the adjacent crosstalk is less than -16 dB. The AWG device occupies an area of 7.5 × 15 mm(2). PDMS AWG has the potential for integration with microfluidics in a monolithic PDMS lab-on-a-chip device for visible light spectroscopy applications.

The authors present a microfluidic device towards an integrated patch-clamping assay. The device replaces conventional glass patch pipette with a buried microfluidic channel on silicon substrate. The microchannel fabrication involves reforming doped glass under heat and pressure, a process, in principle, analogous to the heat-pulling/polishing of glass patch pipettes. Unlike etching substrate, this process leaves a smooth glass surface for seal formation with cell membrane. The microchannel is evolved from a trapped void inside the trench during nonconformal deposition of the doped glass. The results of seal formation with mammalian cells captured at such microchannel opening are presented.