Sensitive Optical Detection Research Articles

Chiral zeolite beta used as stationary phase for enantioseparation in miniaturized open tubular capillary electrochromatography with amperometric detection

BackgroundWith the rapid growth of the demand for optically pure compounds in the fields of biology, medicine and stereospecific synthesis, it is of great importance to develop efficient, economical, simple enantioseparation and analysis methods. Open tubular capillary electrochromatography (OT-CEC) has attracted much attention in the field of chiral separation, but its column capacity and the sensitivity of common-used optical detection are relatively low. Zeolite beta nanomaterial is both enantioselective and size-selective, providing suitable chiral microenvironment for chiral recognition, and amperometric detection (AD) avoids the low sensitivity caused by the short optical path in optical detection to some extent. ResultsZeolite beta nanomaterials with different particle sizes (25, 50 and 200 nm) were synthesized, and the morphology and structure were characterized by scanning electron microscopy and X-ray diffraction. Then, a novel chiral OT column was prepared by one-step method using zeolite beta nanomaterial as chiral stationary phase, and its separation performance was characterized by miniaturized CEC with AD (mini-CEC-AD) device. Under the optimum conditions, six groups of chiral drugs achieved baseline separation. Norepinephrine enantiomers were used for evaluating the inter-day, intra-day and inter-column reproducibility of the prepared open-tubular column. The relative standard deviations of migration time, peak area, resolution and selectivity factor were within 8.7 %. The limits of detection for norepinephrine enantiomers were 0.18 μg mL−1 (S/N = 3), and the average recoveries were in range of 96.7–105.0 %. This developed method has been successfully applied to the analysis of impurity enantiomer in potassium dichromate (+)-norepinephrine injection sample. SignificanceZeolite beta nanomaterial was used as the stationary phase to prepare chiral OT columns for the first time, and this one-step preparation method is simple and easy. The introduction of zeolite beta enriches the types of chiral stationary phase materials in electrochromatographic columns, and mini-OT-CEC-AD system provides an alternative for fast enantioseparation of chiral compounds.

Simple fluorochromic detection of chromium with ascorbic acid functionalized luminescent Bio-MOF-1.

The bioaccumulation of various heavy metals in the environment and agriculture is posing serious hazards to human health. Hexavalent chromium is one of the most encountered heavy metal pollutants. The routine monitoring of Cr(VI) via simple methods assumes great analytical significance in sectors like environmental safety, food quality, etc. This study reports a novel biocompatible and luminescent metal-organic framework (ascorbic acid functionalized Bio-MOF-1) based "Turn-on" nanoprobe for rapid and sensitive optical detection of Cr(VI). Bio-MOF-1 has been synthesized, functionalized with ascorbic acid (AA), and then comprehensively characterized for its key material properties. The presence of Cr(VI) results in the photoluminescence recovery of Bio-MOF-1/AA. Using the above approach, Cr(VI) is detected over a wide concentration range of 0.02 to 20 ng mL-1, with the limit of detection being 0.01 ng mL-1. The nanoprobe is capable of detecting Cr(VI) in real water as well as in some spiked food samples. Hence, the ascorbic acid functionalized Bio-MOF-1 nanoprobe is established as a potential on-field detection tool for Cr(VI).

Research on temperature and pressure interference in photoacoustic spectroscopy gas detection

AbstractPhotoacoustic spectroscopy (PAS) is a highly sensitive optical detection technique for trace gases. However, PAS is sensitive to environmental factors such as temperature and pressure during actual measurement. In this paper, we study the interference characteristics of temperature and pressure in PAS gas detection. The influence of pressure and temperature on PAS is theoretically analyzed based on the basic principle of gas photoacoustic spectroscopy. The effect of different pressure and temperature conditions on the resonance frequency and signal amplitude of PAS is studied through COMSOL software simulation and validated through experiments. Results show that changes in temperature and pressure will affect the resonance frequency and signal amplitude of PAS, thereby impacting the system's sensitivity and accuracy. To reduce the impact of temperature on the PAS sensor, a temperature compensation model was derived based on experimental analysis. Real‐time temperature detection is used to compensate for the photoacoustic signal based on temperature changes, which can improve the accuracy and stability of photoacoustic spectroscopy gas detection. For 5% CO2, the photoacoustic signal and experimental temperature data were measured for 3612 s, and after temperature compensation, the detection limit was 0.0192% at an integration time of 365 s, which is 0.0128% higher than before temperature compensation. The system's normalized noise equivalent absorption coefficient is 3.30 × 10−8 cm−1 WHz−1/2. This research improves the accuracy and reliability of photoacoustic spectroscopy gas detection technology and provides useful references for temperature correction in similar gas detection fields.

Confined assembly of size-tunable silver nanoprisms on flexible Teflon tapes as highly active SERS hotspots for ultralow-level sensing of DNA and glucose

The design of smart and advanced sensors facilitates highly sensitive optical detection platforms for biomolecules. Herein, we attempted the confined assembly of silver nanoprisms (SNPs) on hydrophobic Teflon tapes to design a highly flexible and ultrasensitive biosensing platform for DNA and glucose. We investigated the sensor characteristics including morphological, optical, and SERS activities as a function of nanoparticle size. Pyramidal SNPs were synthesized, whose size was tuned by varying the bromide ion concentrations. The size of SNPs was decreased with an increase in bromide ion concentrations, where quasi-spherical nanoparticles were formed at higher bromide content. The hydrophobic Teflon surface caused considerable constrain during the evaporation of nanoparticle suspension, leading to highly confined SNPs. SERS activities of Teflon/SNP sensors were tuned by varying the size of SNPs, where a size of ∼34 nm exhibited the highest signal enhancement. The optimum Teflon/SNP sensor showed an enhancement factor of 1.3 × 109 with high stability and excellent reproducibility. Teflon/SNP sensor was further exploited to detect DNA and glucose in a label-free method, exhibiting sensitivities of approximately 13.6 fg/µL and 5 µM, respectively. Real-time monitoring of DNA and glucose from saliva was also investigated. Teflon/SNP substrates were found to be excellent biosensing platforms for ultralow-level sensing of biomolecules in a rapid and cost-effective manner.

Sensitive and Compact Evanescent-Waveguide Optical Detector for Sugar Sensing in Commercial Beverages.

This work presents a compact and sensitive refractive index sensor able to evaluate the concentration of an analyte in a sample. Its working principle leverages on the changes in the optical absorption features introduced by the sample itself on the evanescent waves of a light beam. The device's high compactness is achieved by embedding the sample-light interaction site and the detector in a 1 cm2 glass substrate, thanks to microelectronics technologies. High sensitivity is obtained by employing a low-noise p-i-n hydrogenated amorphous silicon junction, whose manufacture process requires only four UV lithographic steps on a glass substrate, thus ensuring low production costs. The system's capabilities are investigated by sensing the sugar content in three commercial beverages. Sensitivities of 32, 53 and 80 pA/% and limits of detection of 47, 29 and 18 ppm are achieved. The above performance is comparable with state-of-the-art results available in the literature, where more complex optical setups, expensive instrumentation and bulky devices are used.

Rapid screening of Turkey DNA fingerprint using highly sensitive label free plasmonic SERS biosensor

Meat adulteration has been raised posing serious impact on human health upon consumption. In particular, Turkey meat being low-cost is added in higher volume with duck and goose meat to gain profit. Herein SERS (surface enhanced Raman spectroscopy) being a highly sensitive optical detection technique is adopted to target label free Turkey DNA sensing. Pulsed laser deposition was utilized to fabricate various metallic nanomaterial aggregates (Ag, Au, Cu, Al) on solid substrates of Quartz and Si at constant number of laser ablations (3000NLP). The fabricated SERS biosensors are characterized for their structural, morphological and optical properties. Based on their characteristics of metallic nanomaterials, the SERS properties are explained in detail with probe molecule Rhodamine 6 G (R6G). The experimental scrutinization was correlated and validated with Finite difference time domain (FDTD) simulations. Amongst all the nanomaterials, Au/Si was found to possess enhanced sensing (Au/Q:2.8 × 107 & Au/Si:3.9 × 107) with the adopted PLD strategy. Au/Si SERS biosensor was projected with label free turkey DNA sensing which was considered as a major food adulterant with other meat types. The developed Au/Si SERS label free biosensor offers high stability, reproducibility as well ultra-sensitivity with turkey DNA sensing down to 1.8 fg/uL.

Highly sensitive and reliable optical fiber TDLAS gas detection system for methane in situ monitoring in near space.

A highly sensitive and reliable tunable diode laser absorption spectroscopy gas detection system with a temperature-pressure compensation algorithm is demonstrated for detecting C H 4 concentrations in near space. Near space generally refers to the airspace 20-100km away from the ground, where temperature and pressure changes are complex. Since the gas absorption spectrum is easily affected by temperature and pressure, a temperature-pressure compensation algorithm is proposed and used in the C H 4 sensor to improve the detection accuracy of the sensor. First, we measured the basic characteristics of the sensor in the laboratory, such as linearity and long-term stability. Experimental results showed that the linear correlation coefficient R-square can reach 0.999, and the concentration fluctuation of C H 4 is less than 0.17ppm within 3.5h. Then the sensor was applied to a research activity in Qinghai Province, China, in September, and the results show that the sensor can effectively monitor the C H 4 concentration in near space.

Highly sensitive light-induced thermoelastic spectroscopy oxygen sensor with co-coupling photoelectric and thermoelastic effect of quartz tuning fork

A light-induced thermoelastic spectroscopy (LITES) gas detection method based on CH3NH3PbI3 perovskite-coated quartz tuning fork (QTF) was proposed. By coating CH3NH3PbI3 thin film on the surface of ordinary QTF, a Schottky junction with silver electrodes was formed. The co-coupling of photoelectric effect and thermoelastic effect of CH3NH3PbI3-QTF results in a significant improvement in detection performance. The oxygen (O2) was select as the target analyte for measurement, and experimental results show that compared with the commercial standard QTF, the introduction of CH3NH3PbI3 perovskite Schottky junction increases the 2f signal amplitude and signal-to-noise ratio (SNR) by ∼106 times and ∼114 times, respectively. The minimum detection limit (MDL) of this LITES system is 260 ppm, and the corresponding normalized noise equivalent absorption coefficient (NNEA) is 9.21 × 10−13 cm−1·W·Hz−1/2. The Allan analysis of variance results indicate that when the average time is 564 s, the detection sensitivity can reach 83 ppm. This is the first time that QTF resonance detection has been combined with perovskite Schottky junctions for highly sensitive optical gas detection.

Tunable photoluminescence emission and third order optical nonlinearity in Sm2/3Cu3Ti4O12 ceramics for optical limiting applications

A combined investigation of the photoluminescence and third order optical nonlinearity of polycrystalline samarium copper titanate, Sm2/3Cu3Ti4O12 (SmCTO), is presented in the current work. SmCTO ceramic has been synthesized using a cost-effective solid state reaction method and investigated by means of spectral absorbance (UV-Vis), photoluminescence (PL), X-ray diffraction (XRD), Field Emission Secondary Emission Microscopy (FESEM), energy dispersive X-ray spectrometry (EDAX) and X-ray Photoelectron Spectroscopy (XPS). From the PL spectra, it is clear that the blue band is due to the TiO6 cluster with oxygen vacancy of the Cu+ type and is assigned to the shallow defects. The green band obtained is due to the reduction in the density of trapped charges as well as particle size. The orange to red emission band corresponds to the charge transfer to the TiO6 cluster with oxygen vacancy of doubly ionized ions. Thus, we can infer the presence of defects like oxygen vacancies (Vox,Vo•,andVo••) in SmCTO. The third order nonlinear absorption coefficient measured by employing the open aperture Z-scan technique shows high values of the order of 10−8 cm/W and 10−4 cm/W, for pulsed and continuous wave lasers, respectively. This is primarily due to the effect of strong excited state absorption, which leads to excellent optical limiting behaviour. Therefore, these materials can be used to make optical limiting devices which can protect human eyes and sensitive optical detectors from dangerous laser beams. The PL and nonlinear optical studies reveals that SmCTO ceramics are practically useful for photonic applications.

SPECTRA: A Novel Compact System for Surface Plasmon Resonance Measurements.

Surface plasmon resonance (SPR) is a common and useful measurement technique to perform fast and sensitive optical detection. SPR instrumentations usually comprise optical systems of mirrors and lenses which are quite expensive and impractical for point-of-care applications. In this work, we presented a novel and compact SPR device called SPECTRA, designed as a spectrophotometer add-on with a grating coupling configuration. The device is conceived as a marketable solution to perform quick SPR measurements in grating configuration without the requirement of complex instrumentation. The device can be customized either in a vertical structure to reach lower incident light angles, or in a horizontal configuration, which is suitable for SPR analysis using liquid solutions. The SPECTRA performance was evaluated through SPR measurements in typical applications. The vertical SPECTRA system was employed to detect different functionalization molecules on gold 720 nm-period grating devices. Meanwhile, the horizontal SPECTRA configuration was exploited to carry out fluid-dynamic measurements using a microfluidic cell with glycerol solutions at increasing concentrations to account for different refractive indexes. The experimental tests confirmed that the SPECTRA design is suitable for SPR measurements, demonstrating its capability to detect the presence of analytes and changes in surface properties both in static and dynamic set-ups.

High-Sensitivity and Direction Recognizable SPR Microdisplacement Sensor Based on Fiber V-Groove

It is difficult to further improve the sensitivity of fiber surface plasmon resonance (SPR) microdisplacement sensor, and it is also unable to identify the direction of microdisplacement. In this article, a high-sensitivity direction recognizable SPR microdisplacement sensor based on fiber V-groove was designed and fabricated. By CO2 laser, the V-groove was fabricated on the graded index multimode fiber, and the SPR effect was produced on the inclined plane of the sensing area by the microdisplacement beam. By controlling the flare angle of the fabricated V-groove, the SPR incident angle was adjusted, so as to effectively increase the microdisplacement sensing sensitivity. The simulation and test results indicate that the sensor with the V-groove flare angle of 88° has the wavelength average sensitivity of 5.26 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> and the intensity average sensitivity of 0.032 a.u./ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> . In order to solve the problem of microdisplacement direction identification, a dual V-groove structure microdisplacement sensor was designed and fabricated. When the microdisplacement direction is different, the transmission beam contacts different V-grooves, and the microdisplacement direction can be identified by the moving direction of the resonance valley. The proposed sensor greatly improves the sensitivity of optical fiber SPR microdisplacement detection and can identify the direction of microdisplacement, which has the potential application value in the field of precision displacement and positioning.

Enhancing single-molecule sensing and superresolution with DNA nanotech.

In recent years, DNA nanotechnology has matured to enable robust production of complex nanostructures and hybrid materials. We have combined DNA nanotechnology with sensitive optical detection to create functional single-molecule devices that enable new applications in single-molecule biophysics, biosensing and superresolution. To improve the sensitivity of DNA detection assays, we created DNA origami optical antennas for metal enhanced fluorescence. Two gold nanoparticles or nanorods enhance the light-matter interactions of dyes and biomolecular assays placed between them. We first discuss the influence of the metal nanostructure on the photophysical properties of dyes. We then show how single molecules can even be detected on a battery-driven portable smartphone microscope using DNA origami nanoantennas [1]. We further present our work on other biosensing applications of DNA origami as well as the possibility of isotropic nanometric superresolution by combining graphene energy transfer with pMINFLUX and DNA PAINT [2].

Efficient Fault Detection Algorithm in Fiber Optic Communication Systems

Primary concern of optical communication system is the signal loss, which need to be traced precisely to enhance the efficiency of the system. Among numerous available techniques, optical time domain reflectometer (OTDR) is the most suitable one for characterizing and tracing the losses. It measures the fraction of a probe pulse that scatters back from the fiber optic cable. Due to the presence of small levels of backscattering in single-mode fiber at long wavelengths, very sensitive optical detector is necessary to achieve sufficient range performance. In the present research, a novel yet simple approach has been demonstrated to understand the range of optical fiber cable feasibility on fault detection and rectification technique. The actual place of fault is marked with the variation in the measured values of OTDR. Thus, it becomes a difficult task to trace and locate the actual place of fault detection, which leads to an inefficient rectification method. The observed values of OTDR shows a gradual decrease of accuracy in locating the actual place of fault. To resolve these issues, here we try to develop an algorithm which is able to easily and efficiently trace the exact location of fault on earth.

Special issue on enhanced photodynamic therapy: Part II

Special issue on enhanced photodynamic therapy: Part II

Monitoring of time-resolved singlet oxygen luminescence at 1270nm by an optical fiber detection system

Singlet oxygen (1O2) is the main cytotoxic substance in Type II photodynamic therapy (PDT). The luminescence of 1O2 at 1270[Formula: see text]nm is extremely weak with a low quantum yield, making the direct detection of 1O2 at 1270[Formula: see text]nm very challenging. In this study, a set of highly sensitive optical fiber detection system is built up to detect the luminescence of photosensitized 1O2. We use this system to test the luminescence characteristics of 1O2 in pig skin tissue ex vivo and mouse auricle skin in vivo. The experimental results show that the designed system can quantitatively detect photosensitized 1O2 luminescence. The 1O2 luminescence signal at 1270[Formula: see text]nm is successfully detected in pig skin ex vivo. Compared with RB in an aqueous solution, the lifetime of 1O2 increases to [Formula: see text]s in pig skin tissue ex vivo. Experiments on living mice suggest that an enhancement of 1O2 intensity with the increase of the TMPyP concentration. When the dose is 25[Formula: see text]mg/kg, the vasoconstriction can reach more than 80%. The results of this study hold the potential application for clinical PDT dose monitoring using an optical fiber detection system.

A sensitive image-based optical detection of heavy metal ions using green synthesized silver nanoparticles

A sensitive image-based optical detection of heavy metal ions using green synthesized silver nanoparticles

Decorating Zirconium on Graphene Oxide to Design a Multifunctional Nanozyme for Eco-Friendly Detection of Hydrogen Peroxide

Peroxidase enzymes are crucial in analytical chemistry owing to significant peroxide analytes and their key role in hydrogen peroxide (H2O2) detection. Therefore, exploiting appropriate catalysts for the peroxidase like reactions has become crucial for achieving desired analytical performance. Zirconium (Zr) has attracted growing interest, as a safe and stable potential eco-friendly catalyst for various organic transformations that address increasing environmental challenges. Hence, aiming at fast, sensitive and selective optical detection of H2O2, a colorimetric platform is presented here, based on the excellent peroxidase enzyme-like activity of Zr decorated on graphene oxide (GO). The synergistic effect achieved due to intimate contact between an enzyme like Zr and the high surface area 0f GO ensures efficient electron transfer that increases the chemical and catalytic activity of the composite and advances the decomposition of H2O2 into hydroxyl radicals. The designed probe, thus, efficiently catalyzes the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB), via hydroxyl radicals, thereby transforming the colorless TMB into blue oxidized TMB within 2 min. The catalytic mechanism of the Zr-GO enzyme mimic is proposed herein and verified using a fluorescent probe terephthalic acid (TA) and other scavenger experiments. The multifunctional optical probe allows sensitive and highly selective recognition of H2O2 in a linear range from 100 to 1000 µM with a low detection limit of 0.57 µM. Essentially, the direct accessibility of Zr prevents having to use the complicated preparation and purification procedures mostly practiced for conventional biozymes and nanozymes. The devised method offers several gains, including being green and an inexpensive catalyst, having lower LOD, being fast, cost-effective and sensitive, and having selective work-up procedures.

Characterization of Aggregating Agents towards Sensitive Optical Detection of Tryptophan Using Lab-on-a-Chip

The analysis of body fluids is desirable to minimize the invasiveness of diagnostic tests and non-destructive forensic investigations. In this study, surface-enhanced Raman spectroscopy (SERS) is employed for sensitive and reproducible detection of biomolecule focusing on ‘hot spots’ generation and automated flow system. Here, we have demonstrated how the plasmon frequency of nanoparticles can be tuned using different aggregating agents for optimal SERS signals. We have compared the effect of different aggregating agents on silver colloids and the resulting enhancement in Raman signals for Tryptophan which is an important amino acid present as an integral component of various body fluids including blood, saliva, tears, and cerebrospinal fluid. The automated segmented flow system, Lab-on-a-chip (LOC), is employed to trap the analyte in droplets while obtaining reproducible SERS spectra of Tryptophan at μM concentration. Further for a thorough interpretation of enhanced vibrational modes of Tryptophan, a theoretical approach has been applied. By combining both experimental and computational approaches we have identified the most preferable site of Tryptophan for interaction with metal nanoparticles and accurately assigned the enhanced Raman bands. The present study demonstrates that the union of SERS and microfluidics has the potential for spectral fingerprinting of biomolecules present in body fluids with high sensitivity.

A light-activated magnetic bead strategy utilized in spatio-temporal controllable exosomes isolation.

Tumor-derived exosomes are considered as a key biomarker in the field of liquid biopsy. However, conventional separation techniques such as ultracentrifugation, co-precipitation and column chromatography cannot isolate samples with high throughput, while traditional immunomagnetic separation techniques, due to steric effect of magnetic beads, reducing sensitivity of exosomes optical detection. Herein, we provide a novel and simple nanoplatform for spatiotemporally controlling extraction and elution of exosomes via magnetic separation and light-activated cargo release. In this system, magnetic beads are co-modified by photoresponsive groups -nitrobenzyl group and aptamers that are compatible with CD63-a highly expressed exosomal surface-specific protein. Through exosomes extracted from cell model and nude mice xenograft tumor model morphological characterization and proteomic analysis, results showed that our novel magnetic bead system outperformed current ultracentrifugation in serum exosome extraction in terms of extraction time, yield, and proportion of populations with high CD63 expression. This strategy may be a powerful tool for exosome isolation in clinical liquid biopsies of cancer disease.

Exploring the Role of 2D-Graphdiyne as a Charge Carrier Layer in Field-Effect Transistors for Non-Covalent Biological Immobilization against Human Diseases.

Graphdiyne's (GDY's) outstanding features have made it a novel 2D nanomaterial and a great candidate for electronic gadgets and optoelectronic devices, and it has opened new opportunities for the development of highly sensitive electronic and optical detection methods as well. Here, we testified a non-covalent grafting strategy in which GDY serves as a charge carrier layer and a bioaffinity substrate to immobilize biological receptors on GDY-based field-effect transistor (FET) devices. Firm non-covalent anchoring of biological molecules via pyrene groups and electrostatic interactions in addition to preserved electrical properties of GDY endows it with features of an ultrasensitive and stable detection mechanism. With emerging new forms and extending the subtypes of the already existing fatal diseases, genetic and biological knowledge demands more details. In this regard, we constructed simple yet efficient platforms using GDY-based FET devices in order to detect different kinds of biological molecules that threaten human health. The resulted data showed that the proposed non-covalent bioaffinity assays in GDY-based FET devices could be considered reliable strategies for novel label-free biosensing platforms, which still reach a high on/off ratio of over 104. The limits of detection of the FET devices to detect DNA strands, the CA19-9 antigen, microRNA-155, the CA15-3 antigen, and the COVID-19 antigen were 0.2 aM, 0.04 pU mL-1, 0.11 aM, 0.043 pU mL-1, and 0.003 fg mL-1, respectively, in the linear ranges of 1 aM to 1 pM, 1 pU mL-1 to 0.1 μU mL-1, 1 aM to 1 pM, 1 pU mL-1 to 10 μU mL-1, and 1 fg mL-1 to 10 ng mL-1, respectively. Finally, the extraordinary performance of these label-free FET biosensors with low detection limits, high sensitivity and selectivity, capable of being miniaturized, and implantability for in vivo analysis makes them a great candidate in disease diagnostics and point-of-care testing.