Meizhen Huang

Urine surface-enhanced Raman spectroscopy for non-invasive diabetic detection based on a portable Raman spectrometer

A feasibility study for non-invasive diabetic detection based on a low cost portable Raman spectrometer and urine surface-enhanced Raman spectroscopy (SERS) is presented. SERS of 41 urine samples (20 diabetic patients and 21 healthy volunteers) mixed with silver nanoparticles are measured by a self-developed portable Raman spectrometer (Hx-Spec) which is excited by a 785 nm diode laser and the spectrum range is 200–2700 cm−1 with a resolution (FWHM) of 6 cm−1. By methods of principal components analysis and linear discriminant analysis, a diagnostic sensitivity of 85% and a specificity of 90.5% are achieved in separating diabetic samples from normal urine specimens. The corresponding receiver operating characteristic is 0.836, indicting the accuracy of the predictive model.

Determination of trace chromium (VI) using a hollow-core metal-cladding optical waveguide sensor

A biosensor capable of highly sensitive detection of trace chromium (VI) with a simple hollow-core metal-cladding waveguide (HCMW) structure is theoretically modeled and experimentally demonstrated. Owing to the high sensitivity of the excited ultrahigh-order modes in the waveguide, a tiny variation of the extinction coefficients in the waveguide guiding layer where the chromate ions reacts with the diphenylcarbazide (DPC) can lead to a significant change of light intensity in the reflection spectrum. The experimental results indicate that using the proposed method, the chromium (VI) sensitivity detection limit can be as low as 1.2 nM, which represents a 16-fold improvement compared to the surface plasmon field-enhanced resonance light scattering (SP-RLS) method, and a 4-fold improvement compared to the flame atomic absorption spectrometry and fluorimetry spectroscopy, respectively.

Reflection-type space-division optical switch based on the electrically tuned Goos–Hänchen effect

A reflection-type space-division optical switch is theoretically proposed and experimentally demonstrated based on the electrically tuned Goos?H?nchen effect in a symmetrical metal-cladding waveguide which employs the PMN?PT ceramics as the guiding layer. Owing to the high sensitivity of the ultrahigh-order modes, the variation of refractive index and thickness induced by the exertion of the controlled voltage on the PMN?PT ceramics will easily give rise to a change in the position of the reflected light. In the experiment, a three-pinhole array is put in the reflected light path and a one-to-three optical switch is achieved. The switching time for 10%?90% light intensity change and the optical crosstalk are measured to be lower than 1.63??s and ?29?dB, respectively. Since the Goos?H?nchen shift can reach approximately 1?mm, the number of output ports can be further increased on condition that the utilized incident light has a smaller spot diameter.

Simultaneous measurement of electro-optical and converse-piezoelectric coefficients of PMN-PT ceramics

A new scheme is proposed to measure the electro-optical (EO) and converse-piezoelectric (CPE) coefficients of the PMN-PT ceramics simultaneously, in which the PMN-PT ceramics acts as the guiding layer of a symmetrical metal-cladding waveguide. As the applied electric field exerts on the waveguide, the effective refractive index (RI) (or synchronous angle) can be effectively tuned from a selected mode to another adjacent mode owing to the high sensitivity and the small spacing of the ultra-high order modes. Subsequently, a correlation between EO and CPE coefficients is established. With this correlation and the measurement of the effective RI change to the applied voltage, the quadratic EO and CPE coefficients of PMN-PT ceramics are obtained simultaneously. The obtained results are further checked by fitting the variations of effective RI to a quadratic function. Our measurement method can be extended to a wide range of other materials.

Nonvolatile and tunable switching of lateral photo-voltage triggered by laser and electric pulse in metal dusted metal-oxide-semiconductor structures.

Owing to the innate stabilization of built-in potential in p–n junction or metal-oxide-semiconductor structure, the sensitivity and linearity of most lateral photovoltaic effect (LPE) devices is always fixed after fabrication. Here we report a nonvolatile and tunable switching effect of lateral photo-voltage (LPV) in Cu dusted ultrathin metal-oxide-semiconductor structure. With the stimulation of electric pulse and local illumination, the sensitivity and linearity of LPV can be adjusted up and down in a nonvolatile manner. This phenomenon is attributed to a controllable change of the Schottky barrier formed between the metal layer and silicon substrate, including the consequent change of film resistivity. This work may widely improve the performance of existing LPE-based devices and suggest new applications for LPE in other areas.

Development of a new signal processor for tetralateral position sensitive detector based on single-chip microcomputer

An inherently nonlinear relation between the output current of the tetralateral position sensitive detector (PSD) and the position of the incident light spot has been found theoretically. Based on single-chip microcomputer and the theoretical relation between output current and position, a new signal processor capable of correcting nonlinearity and reducing position measurement deviation of tetralateral PSD was developed. A tetralateral PSD (S1200, 13×13mm2, Hamamatsu Photonics K.K.) was measured with the new signal processor, a linear relation between the output position of the PSD, and the incident position of the light spot was obtained. In the 60% range of a 13×13mm2 active area, the position nonlinearity (rms) was 0.15% and the position measurement deviation (rms) was ±20μm. Compared with traditional analog signal processor, the new signal processor is of better compatibility, lower cost, higher precision, and easier to be interfaced.

Multiple myeloma detection based on blood plasma surface-enhanced Raman spectroscopy using a portable Raman spectrometer

The feasibility of surface enhanced Raman spectroscopy (SERS) for multiple myeloma (MM) detection is investigated in this work. SERS measurements of silver nanoparticle mixed blood plasma samples are performed using a low-cost and portable Raman spectrometer. The tentative assignment of Raman peaks indicates an increase in amino acids, nucleic acid base content and a decrease in cholesterol ester in the MM group. Combined with the multivariate analysis method of principle component analysis (PCA) and linear discriminate analysis (LDA), a diagnosis result for 32 samples with a sensitivity of 93.75% and specificity of 87.5% is achieved. The performance of the corresponding receiver operating characteristic (ROC) curve is 0.957. It is a potential rapid and non-invasive method for preliminary MM screening.

Enhanced Raman scattering assisted by ultrahigh order modes of the double metal cladding waveguide

Distinguished from the usual strategy to enhance the Raman scattering such as creating hot spots in the surface-enhanced Raman scattering, this paper takes a quite different approach based on the double metal cladding waveguide. The target analyte is located in the guiding layer of sub-millimeter scale, where several ultrahigh order modes with high intensity are simultaneously excited via a focused laser beam. The experimental setup is simple, and both simulation and experimental results confirm the enhancement mechanism of these oscillating modes. Other appealing features include the large detection area and the ability to excite guided modes via both polarizations. This scheme can be applied to large molecules detection and readily integrated with other Raman enhancement techniques.

Rapid determination of thiabendazole in juice by SERS coupled with novel gold nanosubstrates

The aim of this study was to develop surface-enhanced Raman spectroscopy (SERS) methods in combination with novel gold nanomaterial-based substrates for rapid measurement and quantification of pesticides extracted from lemon, carrot, and mango juice. Facile synthesis of a sensitive and robust SERS substrate was achieved by assembling gold nanorods (AuNRs) into vertically aligned arrays on silicon slides. The nanorod arrays were orderly aligned and can induce vigorous electromagnetic field for SERS measurement. The synthesized SERS substrate was utilized for detection and quantification of thiabendazole in juice samples using partial least squares analysis with R values of 0.99, 0.98, and 0.99 for lemon, carrot, and mango juice, respectively. The detection limits of thiabendazole were 149, 216, and 179 μg/L in lemon, carrot, and mango juice, respectively. These results demonstrate that SERS combined with AuNR substrates is a quick, convenient, and highly sensitive technique for detection of thiabendazole residues in fruits juice.

Facile synthesis of cellulose nanofiber nanocomposite as a SERS substrate for detection of thiram in juice

There has been growing interest in the use of nanocellulose-based substrate for surface-enhanced Raman spectroscopy (SERS) applications. This study aimed to use cellulose nanofibers (CNF) to develop novel CNF-based nanocomposite as a SERS substrate. CNF were cationized with ammonium ions and then interacted with citrate-stabilized gold nanoparticles (AuNPs) via electrostatic attraction to form uniform nanocomposites. The CNF-based nanostructures were loaded with AuNPs that were firmly adhered on the CNF surfaces, providing a three-dimensional plasmonic SERS platform. A Raman-active probe molecule, 4-aminothiophenol, was selected to evaluate the sensitivity and reproducibility of CNF-based SERS substrate. The intensity of SERS spectra obtained from CNF/AuNP nanocomposite was 20 times higher than that from the filter paper/AuNP substrate. The SERS intensity map demonstrates good uniformity of the CNF/AuNP substrate. CNF/AuNP nanocomposites were used in rapid detection of thiram in apple juice by SERS and a limit of detection of 52 ppb of thiram was achieved. These results demonstrate that CNF/AuNP nanocomposite can be used for rapid and sensitive detection of pesticides in food products.