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Device performance of standard strip, slot and hybrid plasmonic ??-ring resonator: a comparative study
摘要： In this paper, we presented three μ-ring resonator structures based on the standard strip, slot and hybrid plasmonic waveguides based on the SOI platform. A standard strip waveguide is formed by depositing a silicon core on a silica substrate. Whereas the slot waveguide is tailored by keeping a narrow air gap between two silicon strip waveguides. Finally, the hybrid plasmonic waveguide is composed of Metal-Air-Silicon structure, where the E-field is significantly enhanced in the narrow air gap. The ring radius is kept at 1.5 μm for the three designs. The transmission spectrum and E-field distribution of these structures are simulated using the finite element method (FEM). Silicon strip waveguide-based ring resonators are easy to fabricate but their sensitivity is quite low as compared to the other two designs. μ-ring resonator based on hybrid plasmonic waveguide shows the best sensitivity of 333.3 nm/RIU. While, slot waveguide based μ-ring resonator showed the best performance in the quality factor, the figure of merits and limit of detection. We believe that this comparative study will facilitate the researchers to choose the suitable waveguide design for ring resonators depending on their preferred application and fabrication technology available.
关键词： Conventional ring resonator,hybrid plasmonic ring resonator,sensitivity,figure of merit,limit of detection,Q-factor,slot ring resonator
更新于2025-09-23 15:19:57
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Simple geometrical modifications for substantial color intensity and detection limit enhancements in lateral-flow immunochromatographic assays
摘要： One of the ongoing challenges in lateral flow Immunochromatographic assays (LFIA), is lowering the limit of detection and enhancing their signal quality, i.e. the color intensity. There are a number of rather costly and complicated processes for this aim, such as the use of functionalized materials/membranes and additional spectroscopic readout units. Nonetheless, there are simple and easy to practice alternatives, to be uncovered by analyzing the essential parameters of immunological reactions. The color intensity of the test line is a function of analytes flow velocity and their reaction rate. Detection pad width and test line position impact the flow velocity and reaction rate kinetics, examined in this paper for the limit of detection (LOD) and test-line color intensity. Firstly, the impact of width on the LOD was examined for human chorionic gonadotropin (pregnancy biomarker). Test line color intensity was measured using five different widths of the detection pad (trapezoidal) and four different test line positions, and the trends observed were explained according to the measured evolution of the velocity along the chromatography paper. With a constant width absorbent pad, LOD was cut by half to 5 mIU/ml by using a narrowing width detection pad, which keeps the wicking velocity higher than normal strips, and compared to them, color intensity increase between 55-150%, depending on the concentration. Nevertheless, a widening detection pad might cut the color intensity up to 150%, compared to normal strips, due to a profound decline of the analyte to ligand ratio at the test line. In addition, adequately sending the test line away from the conjugate pad yields the highest possible color intensity, for up to 400% of increase, in lower concentrations and narrowing test pads. However, further distancing the test line downfalls the color intensity.
关键词： Lateral Flow Immunochromatographic Assays,Trapezoidal Geometry,Limit of Detection,Detection Pad,Capillary Flow Velocity,Porous Medium,Color Intensity,Test Line Displacement
更新于2025-09-19 17:15:36
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Quantitative analysis of Pb in soil by femtosecond-nanosecond double-pulse laser-induced breakdown spectroscopy
摘要： The effects of inter-pulse delay on the quantitative analysis of femtosecond-nanosecond double-pulsed laser-induced breakdown spectroscopy (fs-ns DP-LIBS) for assessing Pb in soil have been systematically studied in this work. A femtosecond pulse laser was focused to produce a filament, which was used to ablate the soil sample and produce an appreciable amount of aerosol particles ejected from the soil surface at a low density. Scattering images of the soil particles ejected from the soil surface were obtained, and the soil particles were found to have a delay of 800 μs. After an inter-pulse delay, a nanosecond Nd:YAG laser re-ablated the soil particles and obtained a spectral enhancement and a narrow line width. The quantitative analysis based on DP-LIBS for Pb in soil was strongly dependent on the inter-pulse delay time. With an inter-pulse delay time of 10 μs for DP-LIBS, the R-square factor (R2), relative standard deviation (RSD), root mean square error of cross-validation (RMSECV), and limit of detection (LOD) were 99.42%, 2.99%, 0.42 wt.%, and 8.13 mg/kg, respectively. These findings demonstrate that DP-LIBS can be applied as an efficient spectroscopic tool to improve the quantitative analysis of Pb heavy metal in soil.
关键词： fs-ns DP-LIBS,quantitative analysis,limit of detection,Pb heavy metal
更新于2025-09-19 17:13:59
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Biocompatible Palladium Telluride Quantum Dot-Amplified Biosensor for HIV Drug
摘要： Indinavir (IDV) is a potent and well-tolerated protease inhibitor antiretroviral (ARV) drug used as a component of the highly active antiretroviral therapy (HAART) of human immunodeficiency virus (HIV). It undergoes hepatic first-pass metabolism that is catalysed by microsomal cytochrome P450-3A4 enzyme (CYP3A4), which results in pharmacokinetics that may be favourable or adverse. Therapeutic drug monitoring (TDM) of IDV during HIV treatment is therefore critical, in order to prevent the adverse effects of its first-pass metabolism and optimise an individual’s dosage regime. Biosensors are now the preferred diagnostic tools for TDM assessment at point-of-care, due to their high sensitivity and real-time response. An electrochemical biosensor for IDV was prepared by depositing a thin film of CYP3A4 (a thiolate enzyme) and thioglycolic acid-capped palladium telluride quantum dot (TGA-PdTeQD) on a cysteamine-functionalised gold disk electrode (Cyst|Au) using a combination of thiol and carbodiimide covalent bonding chemistries. The electrochemical signatures of the biosensor (CYP3A4|TGA-PdTeQD|Cyst|Au) were determined by cyclic voltammetry (CV) that was performed at a scan rate of 500 mV s?1, and the sensor responses at the characteristic reduction peak potential value of ? 0.26 V were recorded. The sensitivity, linear range (LR) and limit of detection (LOD) values of the indinavir biosensor were 4.45 ± 0.11 μA nM?1 IDV, 0.5–1.0 nM IDV (i.e. 3.6 × 10?4–7.1 × 10?4 mg L?1 IDV) and 4.5 × 10?4 mg L?1 IDV, respectively. The values of the two analytical parameters (LR and LOD) of the biosensor were by up to four orders of magnitude lower than the maximum plasma concentration (Cmax) values of indinavir (0.13–8.6 mg L?1 IDV). The IDV biosensor was successfully used to detect IDV in human serum samples containing dissolved indinavir tablet. This, therefore, indicates the indinavir biosensor’s suitability for TDM applications, using samples obtained within 1–2 h of drug intake at point-of-care, for which very low levels of the drug are expected.
关键词： Human serum,Limit of detection,Indinavir,Palladium telluride quantum dot,Cyclic voltammetry,Electrochemical sensors,Cytochrome P450-3A4
更新于2025-09-16 10:30:52
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Multivariate determination of 10B isotopic ratio by laser-induced breakdown spectroscopy using multiple BO molecular emissions
摘要： Measurements of boron isotopic ratios have been investigated using LIBS, and combined LIBS and Molecular laser-induced fluorescence (MLIF). Mixtures of various ratios of research grade H3 11BO3 and H3 10BO3 in pellet form were interrogated with a Q-switched Nd:YAG laser operating at 532 nm. The resulting plasma was examined for their BO molecular bands in the 254–262 nm and 266–276 nm wavelength ranges. A minimum of three band heads of the β system B2Σ → X2Σ transitions were identified. The rovibronic isotopic shifts of the corresponding bands were measured and were conclusively compared to the literature. MLIF was applied to LIBS emission lines covering 253–271 nm to enhance some band heads, selectively. Both LIBS and LIBS-MLIF emissions were subject to multivariate statistical analysis to predict 10B isotopic ratios. Two PLS regression calibration models were examined to better examine the effects, sensitivity, accuracy of the laser-produced plasma excitation modalities based models through the figure of merit. For the full calibration set (21 samples), the root mean square error of cross-validation (RMSECV), the pseudo univariate LOD (LODpu) and the LOD interval ([LODmin, LODmax]) for 10B isotopes were improved from 1.61%, 4.81%, [2.64%, 3.49%] 10B isotopic ratio, respectively for LIBS to 0.98%, 2.40%, [2.19%, 2.81%] 10B isotopic ratio, respectively for LIBS-MLIF. However, using a random subset of the samples (14) as a calibration set and the rest as a test set, the root mean square error of prediction of 10B isotopic ratio in the test set improved from 2.95% to 1.16% 10B isotopic ratio, respectively for LIBS and LIBS-MLIF; and the LOD interval improved from [2.45%, 2.69%] to [1.88%, 2.12%] 10B isotopic ratio when calculated with cross-validated residual variance. Moreover, the prediction error of a test set improved from 2.95% for LIBS to 1.16% for LIBS-MLIF.
关键词： Molecular laser-induced fluorescence,LIBS-MLIF,Limit of detection interval,Laser-induced breakdown spectroscopy,Boron isotopes,Molecular band
更新于2025-09-16 10:30:52
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Speed and sensitivity – Integration of electrokinetic preconcentration with a leaky waveguide biosensor
摘要： Improving the limit of detection by preconcentration and reducing the response time of optical biosensors are key requirements to enable their use in point of care (PoC) applications. To address these requirements, we have shown that integration of isoelectric focusing (IEF) at a pH step with a leaky waveguide (LW) sensor containing a non-speci?c a?nity ligand (reactive blue 4 dye (RB4)) can reduce the limit of detection of an exemplar protein (bovine serum albumin (BSA)) by a factor of 600–930 and reduce the response time to < 60 s. This is 6–9 times better preconcentration and up to 16 times faster response time than previous reports. IEF was performed with standard ampholytes and with simple acids and bases forming a pH step. Using ampholytes gave good preconcentration, but was much slower than using a pH step. The LW sensor used a thin agarose hydrogel layer into which RB4 was immobilized. The dye acted both as a non-speci?c a?nity ligand and to visualize the waveguide resonances. This allowed the refractive index of the waveguide to be monitored in real time at any point along the 10 mm separation channel length.
关键词： Response time,Electrokinetic preconcentration,Limit of detection,Leaky waveguide,Point-of-care
更新于2025-09-16 10:30:52
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Ovalbumin antibody-based fluorometric immunochromatographic lateral flow assay using CdSe/ZnS quantum dot beads as label for determination of?T-2 toxin
摘要： This work describes an anti-ovalbumin antibody-based lateral flow immunoassay (LFI) for T-2 toxin. The antibody uses a coating antigen as a bifunctional element for universality and introduces preincubation to improve the detection limits of the method. T-2 toxin and ovalbumin-modified T-2 toxin competitively binds on the anti-T-2 toxin monoclonal antibody modified on CdSe/ZnS quantum dot beads during preincubation. The modified T-2 toxin acts as a bifunctional element that forms immuno complexes during preincubation and combines with anti-ovalbumin antibody coated in the test line through the ovalbumin terminal. Fluorescence is detected at 610 nm on the test zone following photoexcitation at 365 nm. It has a reverse dose-effect relationship with the amount of T-2 toxin. The calibration plot is linear in the 20–110 fg mL?1 T-2 toxin concentration range, and the limit of detection (LOD) is 10 fg mL?1, which is lower by 8-fold than that of the traditional LFI system (LOD 80 fg mL?1) and one order of magnitude than those of LFIs with labels of colloidal gold nanoparticles (LOD 150 fg mL?1) or fluorophores (LOD 190 ng mL?1). Universality was verified through aflatoxin B1 detection using the established ovalbumin antibody-based LFI system (LOD 10 fg mL?1). The performance of the method was compared with that of established systems and a commercial ELISA kit (LOD 360 fg mL?1).
关键词： Fluorometry,Bifunctional element,Calibration plot,Sensitivity,Limit of detection,Aflatoxin B1,Preincubation
更新于2025-09-11 14:15:04
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A high sensitive SH-SAW biosensor based 36° Y-X black LiTaO3 for label-free detection of Pseudomonas Aeruginosa
摘要： A label-free and high sensitive shear horizontal surface acoustic wave (SH-SAW) biosensor for the nucleic acid detection of Pseudomonas Aeruginosa was developed in this work. An effective detection cell was fabricated by dint of acrylic material. The base frequency of the SH-SAW biosensor fabricated on 36°Y-X rotated black LiTaO3 piezoelectric substrate was 210 MHz. The self-assembled monolayer was formed on the gold surface of the sensitive area, and the increase of mass loading in the sensitive area leads to phase shift of SH-SAW. In this work, the detection limit has been improved by 3–4 times than that in our previous works, which is 1 nmol/L for the nucleic acid of the Pseudomonas Aeruginosa. And the phase shifts related to detection sensitivity are also elevated to 4 ° after the specific binding of the ss-DNA probes and the complementary sequences. In this study, the plot of phase shift against the logarithm of concentration of Pseudomonas aeruginosa nucleic acid was found to be linear over the range from 0.1 nmol/L to 1000 nmol/L with a correlation coefficient 0.98777. The detection limit as low as 0.28 nmol/L was achieved for Pseudomonas aeruginosa nucleic acid in this paper.
关键词： SH-SAW,Biosensor,Black LiTaO3,Limit of detection,Phase shift
更新于2025-09-11 14:15:04
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[ACS Symposium Series] Raman Spectroscopy in the Undergraduate Curriculum Volume 1305 || Exploring the Figures of Merit of Surface-Enhanced Raman Spectroscopy
摘要： This undergraduate laboratory experiment is designed to help students gain a deeper understanding of surface-enhanced Raman spectroscopy (SERS). Students will learn to fabricate nanoparticles, obtain Raman and SERS data, construct calibration curves, and determine the signal-to-noise ratio, limit of detection, and coefficient of variation of alizarin, a dye molecule commonly found in cultural heritage materials. Overall, the laboratory experiment will provide an opportunity for students to develop laboratory skills in nanoscience and spectroscopy and further develop their critical thinking skills.
关键词： SERS,surface-enhanced Raman spectroscopy,limit of detection,calibration curves,alizarin,signal-to-noise ratio,nanoparticles,coefficient of variation
更新于2025-09-09 09:28:46
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Nitric Oxide Detector Based on WO <sub/>3</sub> -1wt%In <sub/>2</sub> O <sub/>3</sub> -1wt%Nb <sub/>2</sub> O <sub/>5</sub> with State-of-the-Art Selectivity and ppb-Level Sensitivity
摘要： Fast, sensitive, and precise detection of nitric oxide (NO) is critical to many applications in environmental monitoring and early disease diagnosis via respiratory testing. An effective detection system requires a sensor to detect NO gas at the parts per billion (ppb) level, and this system should possess a high degree of anti-interference selectivity. To achieve these targets, a series of gas sensor thin films based on intrinsic WO3, one-additive-doped WO3 (prepared by doping In2O3 or Nb2O5), and two-additive-doped WO3 (synthesized by doping with In2O3 and Nb2O5) oxides were successfully grown. By analyzing the properties of sensitivity, selectivity, responsiveness, and recovery time of the gas sensors, we found that WO3-1wt%In2O3-1wt%Nb2O5 has overwhelming advantages over intrinsic WO3, WO3-In2O3, and WO3-Nb2O5. A sensing response value of 2.4 was observed for NO concentrations as low as 20 ppb from the WO3-1wt%In2O3-1wt%Nb2O5 sensor. With 100 ppb NO gas, the WO3-1wt%In2O3-1wt%Nb2O5 sensor achieved a high response of 56.1 at 70 °C, which is a state-of-the-art performance for NO detection at low working temperature settings. WO3-1wt%In2O3-1wt%Nb2O5 also yields significantly improved selectivity and stability over intrinsic WO3, WO3-In2O3, and WO3-Nb2O5. Studies on the sensing mechanism show that the grain size, rather than the n?n heterostructure effect, plays a dominant role in the observed results. By decreasing the grain size so that it is close to the thickness of the space-charge layer, the sensing response is enhanced. Although room remains to further improve the sensing properties, the performance of WO3-1wt%In2O3-1wt%Nb2O5 is sufficient for implementation in low-content NO detection devices.
关键词： codoping,high selectivity,NO gas sensor,limit of detection (LOD),ppb-level response,pulsed laser deposition (PLD)
更新于2025-09-09 09:28:46