Optoplasmonic Hybrid Materials for Trace Detection of Methamphetamine in Biological Fluids through SERS

A handheld fluorescent lateral flow immunoassay platform for highly sensitive point-of-care detection of methamphetamine and tramadol

The escalating issue of drug abuse poses a significant threat to public health and societal stability worldwide. An on-site drug detection platform is vital for combating drug abuse and trafficking, as it eliminates the need for additional tools, extensive processes, or specialized training. Therefore, it is imperative to develop a fast, sensitive, non-invasive, and reliable multiplex drug testing platform. In this study, we have presented a silica core@dual quantum dot-shell nanocomposite (SI/DQD)-based fluorescent lateral flow immunoassay (LFIA) platform for the highly sensitive and simultaneous point-of-care (POC) detection of methamphetamine (MET) and tramadol (TR). A 3D-printed attachment was designed to integrate optical and electrical components, facilitating the miniaturization of the instrument and reducing both cost and complexity. The device's advanced hardware and effective fluorescence extraction algorithm with waveform reconstruction enable swift, automatic noise reduction and data analysis. SI/DQD nanocomposites were utilized as fluorescent nanotags in the LFIA strips due to their outstanding luminous efficiency and robustness. This LFIA platform achieves impressive detection limits (LODs) of 0.11 ng mL-1 for MET and 0.017 ng mL-1 for TR. The method has also successfully detected MET and TR in complex biological samples, demonstrating its practical application capabilities. The proposed fluorescent LFIA platform, based on SI/DQD technology, holds significant promise for the swift and accurate POC detection of these substances. Its affordability, compact size, and excellent analytical performance make it suitable for on-site drug testing, including at borders and roadside checks, and open up new possibilities for the design and implementation of drug testing methods.

Fabrication of an Optoplasmonic Raft with Improved SERS Performance Detecting Methamphetamine through Bubble Enrichment

In this work, a novel raft-like structure that combines noble metal nanoparticles (NPs) with an interconnected layer of hemispherical dielectric shell was fabricated and characterized. It was discovered that this hybrid material can enhance the optoplasmonic interaction between plasmonic and dielectric components, thereby improving the sensing performance in surface-enhanced Raman spectroscopy (SERS). Varied geometric parameters of the fabricated optoplasmonic raft, including the inner diameter and thickness of the dielectric shell, were attempted and analyzed through numerical simulation and experimental SERS measurements. With particular size, thickness, and incident orientation, the silica shell focuses the incident optical flow into the deposited silver NPs, undergoing similar near-field focusing behavior in comparison with other optoplasmonic entities. This optoplasmonic raft floating on the water surface is able to harvest the target molecules effectively through bubble enrichment, which rapidly captures and concentrates analytes from the aqueous phase. With a limited sampling time, the sensing performance of the developed optoplasmonic raft is improved by applying the optimized parameters involved in bubble enrichment. The substrates and corresponding enrichment method were implemented in the detection of methamphetamine (METH), achieving a limit of detection (LOD) down to 0.035 nM. As for practical onsite detection, the developed substrate and bubbling strategy were applied in an assembled set, employing a portable Raman spectrometer and an air pump. This set is able to detect METH dissolved in regular commercial beer, which is quite competent in the investigation of drug abuse.

Surface-enhanced Raman imaging through sprayed probes for the application in chemical visualization of methamphetamine within fingerprints

For fingerprint-involved forensic investigations, cyanoacrylates and inorganic nanophosphors are mostly used for fingerprint visualization. However, methods to simultaneously report fingerprint images and the corresponding specific chemical information have yet to be realized. In this work, chemical visualization of the analytes in fingerprints is achieved through surface-enhanced Raman spectroscopy (SERS) measurements with the aid of spray-dispersed gold nanorods (AuNRs). The optimal coverage of AuNRs was studied by theoretical simulations and experimental operations. A rapid sampling of fingerprints with the chemical of interest was developed by tuning the spray parameters. In particular, the SERS imaging of methamphetamine in fingerprint latent was attempted by addressing the SERS spectral features of methamphetamine. This chemical visualization method reflects both the graphical and chemical characteristics of fingerprints in a single batch measurement, in which methamphetamine can be detected and mapped at the concentration of 10^-5 M. The data processing approach was also modified by employing relevant logical judgments. The improved SERS images with sharpened patterns of fingerprints were obtained by involving the scored multi-peak judgments.

Nanowire-in-bowl-shaped piezoelectric cavity structure for SERS directional detection of nanoplastics less than 50 nm

The accurate detection of nanoplastics is crucial due to their harmful effects on the environment and human beings. However, there is a lack of detection methods for nanoplastics smaller than 50 nm. In this research, we successfully constructed an Ag/CuO nanowire (NW)/BaTiO₃@Polyvinylidene fluoride (PVDF) Bowl-shaped substrate with a nanowire-in-Bowl-shaped piezoelectric cavity structure that can modulate surface-enhanced Raman scattering (SERS) by the piezoelectric effect by the virtue of the tip effect of the CuO NW and light focusing effect of the Bowl-shaped cavity. Due to its unique nanowire-in-Bowl-shaped structure and piezoelectrically modifiable ability, nanoplastics less than 50 nm were successfully detected and quantitatively analyzed. We believe that the Ag/CuO NW/BaTiO₃@PVDF Bowl-shaped substrate can provide an efficient, accurate, and feasible way to achieve qualitative and quantitative detection of nanoplastics.

A copper foam-based surface-enhanced Raman scattering substrate for glucose detection

Raman spectroscopy can quickly achieve non-destructive, qualitative and quantitative detection, and analysis the molecular structure of substances. Herein, a facile and low-cost method for preparation of highly sensitivity SERS substrates was implemented through the displacement reaction of copper foam immersed in AgNO₃ ethanol solution. Due to the 3D structure of copper film and homogenous displacement, the Ag-Cu substrate showed high performance SERS enhancement (1.25 × 10⁷), and the lowest detection concentration for R6G reached 10^-10 Mol/L. For glucose detection, mixed decanethiol (DT)/mercaptohexanol (MH) interlayer was used to enable glucose attach to the substrate surface, and the limit of detection reached to 1 uM/L. SERS substrate makes the Ag-Cu SERS substrate promising for biological applications.

Plasmon-driven catalytic reactions in optoplasmonic sandwich hybrid structure

As an interesting phenomenon in the field of surface enhanced Raman spectroscopy (SERS), the plasmon-driven catalytic reaction (PDSC) induced by plasmonic hot electrons has great value in the research of novel properties of surface plasmons and accuracy of SERS applications. In this work, an optoplasmonic sandwich hybrid structure is proposed for studying PDSC of p-aminothiophenol (PATP) molecules, which is composed of Au film, metal organic frameworks (MOFs) nanoparticles, zeolithic imidazolate (ZIF-8), and single S i O ₂ microsphere (Au f i l m@M O F s@S i O ₂). In order to analyze the novel, to the best of our knowledge, phenomenon of the PDSC in this micro-nano structure, the hot electron generation in the MOF without the plasmonic core is carried out by combining the plasmonic enhancement of gold film with the light concentration of microspheres. Experimental data show that the PDSC reactions is dependent on the size of the MOFs nanoparticle and the size of the S i O ₂ microsphere, which is confirmed by the electromagnetic field simulation of the finite-difference time-domain method (FDTD). Our work not only strengthens the understanding of surface plasmon in optoplasmonic hybrid structures but also has broad application prospects in the SERS and plasmon-driven catalytic fields.

Vibrational Spectroscopy in Urine Samples as a Medical Tool: Review and Overview on the Current State-of-the-Art

Although known since the first half of the twentieth century, the evolution of spectroscopic techniques has undergone a strong acceleration after the 2000s, driven by the successful development of new computer technologies suitable for analyzing the large amount of data obtained. Today's applications are no longer limited to analytical chemistry, but are becoming useful instruments in the medical field. Their versatility, rapidity, the volume of information obtained, especially when applied to biological fluids that are easy to collect, such as urine, could provide a novel diagnostic tool with great potential in the early detection of different diseases. This review aims to summarize the existing literature regarding spectroscopy analyses of urine samples, providing insight into potential future applications.

Nanomaterials meet surface-enhanced Raman scattering towards enhanced clinical diagnosis: a review

Surface-enhanced Raman scattering (SERS) is a very promising tool for the direct detection of biomarkers for the diagnosis of i.e., cancer and pathogens. Yet, current SERS strategies are hampered by non-specific interactions with co-existing substances in the biological matrices and the difficulties of obtaining molecular fingerprint information from the complex vibrational spectrum. Raman signal enhancement is necessary, along with convenient surface modification and machine-based learning to address the former issues. This review aims to describe recent advances and prospects in SERS-based approaches for cancer and pathogens diagnosis. First, direct SERS strategies for key biomarker sensing, including the use of substrates such as plasmonic, semiconductor structures, and 3D order nanostructures for signal enhancement will be discussed. Secondly, we will illustrate recent advances for indirect diagnosis using active nanomaterials, Raman reporters, and specific capture elements as SERS tags. Thirdly, critical challenges for translating the potential of the SERS sensing techniques into clinical applications via machine learning and portable instrumentation will be described. The unique nature and integrated sensing capabilities of SERS provide great promise for early cancer diagnosis or fast pathogens detection, reducing sanitary costs but most importantly allowing disease prevention and decreasing mortality rates.

Ultrasensitive multiplex SERS immunoassay based on porous Au-Ag alloy nanoparticle-amplified Raman signal probe and encoded photonic crystal beads

An ultrasensitive multiplex surface-enhanced Raman scattering (SERS) immunoassay was developed using porous Au-Ag alloy nanoparticles (p-AuAg NPs) as Raman signal amplification probe coupling with encoded photonic crystal microsphere. p-AuAg NPs were synthesized and modified with the second antibody (Ab₂) and Raman tag (mercaptobenzoic acid, MBA) to prepare a Raman signal-amplified probe. The high porosity of the p-AuAg NPs enables significant coupling of the localized surface plasmon resonance and thus abundant inherent hotspots for Raman signal enhancement. 3D-ordered silver nanoparticles-coated silica photonic crystal beads (Ag/SPCBs) were prepared as encoded SERS substrate for multiplex detection using their reflection peaks. The signal-amplified probe was used for multiplex detection of tumor markers carcinoembryonic antigen (CEA) and alpha fetoprotein (AFP). The wide linear ranges of 10^-7-10³ ng/mL for CEA and 10^-4-10³ ng/mL for AFP with detection limits of 1.22 × 10^-8 ng/mL and 2.47 × 10^-5 ng/mL for CEA and AFP at a signal-to-noise ratio of 3 were obtained. The proposed multiplex SERS immunoassay method displays ultrahigh sensitivity, wide linear range, and excellent specificity, which can be successfully applied to measure clinical serum samples with satisfactory results. The research provides a novel SERS signal enhancement strategy for the multiplex bioassay.

Optoplasmonic MOFs film for SERS detection

Optoplasmonic hybrid structures composed of photonic and plasmonic elements with excellent optical properties are of great significance for the development of surface-enhanced Raman spectroscopy (SERS) substrates. In this work, the optoplasmonic hybrid structure is composed of SiO₂ microsphere and two-dimensional (2D) plasmonic- metal organic frameworks (MOF) film. Among them, the 2D plasmonic-MOF film is prepared from silver nanoparticles encapsulated by zeolitic imidazole acid framework (AgNP@ZIF-8) by self-assembly method. This optoplasmonic hybrid structure with gas adsorption properties could be used as a SERS substrate for 4-Mercaptophenol (4-MP) gas detection. Experimental data show that this substrate is dependent on the thickness of the ZIF shell and the size of the SiO₂ microspheres. In addition, it is confirmed by the electromagnetic field simulation of finite-difference time-domain method (FDTD). The optoplasmonic hybrid microstructures exhibit good uniformity for detection of 4-MP gas molecules. This work not only broadens the understanding of our optoplasmonic hybrid structure, but also has broad application prospects in SERS and gas sensing related fields.

Self-Calibration 3D Hybrid SERS Substrate and Its Application in Quantitative Analysis

Surface-enhanced Raman spectroscopy (SERS) has been widely applied in many fields as a sensitive vibrational fingerprint technique. However, SERS faces challenges in quantitative analysis due to the heterogeneity of hot spots. An internal standard (IS) strategy has been employed for correcting the variation of hot spots. However, the method suffers from limitations due to the competitive adsorption between the IS and the target analyte. In this work, we combined the IS strategy with the 3D hybrid nanostructures to develop a bifunctional SERS substrate. The substrate had two functional units. The bottom self-assembly layer consisted of Au@IS@SiO₂ nanoparticles, which provided a stable reference signal and functioned as the calibration unit. The top one consisted of appropriate-sized Au octahedrons for the detection of target analytes, which was the detection unit. Within the 3D hybrid nanostructure, the calibration unit improved the SERS performance of the detection unit, which was demonstrated by the 6-fold increase of SERS intensity when compared with the 2D substrate. Meanwhile, the reproducibility of the detection was greatly improved by correcting the hot spot changes through the calibration unit. Two biomedical molecules of cotinine and creatinine in ultrapure water and artificial urine, respectively, were sensitively determined by the 3D hybrid substrate. We expect that the developed bifunctional 3D substrate will open up new ways to advance the applications of SERS.

Research Progress of Raman Spectroscopy and Raman Imaging in Pharmaceutical Analysis

The analytical investigation of the pharmaceutical process monitors the critical process parameters of the drug, beginning from its development until marketing and postmarketing, and appropriate corrective action can be taken to change the pharmaceutical design at any stage of the process. Advanced analytical methods, such as Raman spectroscopy, are particularly suitable for use in the field of drug analysis, especially for qualitative and quantitative work, due to the advantages of simple sample preparation, fast, nondestructive analysis speed, and effective avoidance of moisture interference. Advanced Raman imaging techniques have gradually become a powerful alternative method for monitoring changes in polymorph distribution and active pharmaceutical ingredient distribution in drug processing and pharmacokinetics. Surface-enhanced Raman spectroscopy (SERS) has also solved the inherent insensitivity and fluorescence problems of Raman, which has made good progress in the field of illegal drug analysis. This review summarizes the application of Raman spectroscopy and imaging technology, which are used in the qualitative and quantitative analysis of solid tablets, quality control of the production process, drug crystal analysis, illegal drug analysis, and monitoring of drug dissolution and release in the field of drug analysis in recent years.

The finite-difference time-domain (FDTD) guided preparation of Ag nanostructures on Ti substrate for sensitive SERS detection of small molecules

Surface-enhanced Raman Scattering (SERS) has become a powerful analytical technique for highly sensitive detection of target molecules. Its performance, however, is heavily dependent on the substrates. Relatively low sensitivity for small molecules and poor reproducibility in quantitative analysis are often encountered in most of nanoparticle modified SERS substrate. The present work starts by theoretical investigation of the electromagnetic field enhancement by nanomaterials of coinage metals with different sizes. The finite-difference time-domain (FDTD) simulation results revealed that the Ag NPs with the size around 100 nm exhibit the strongest SERS effect and the 'Ag-Ag' gaps have shown higher electromagnetic field enhancement than that of the 'Ag-Ti' gap. Subsequently, a multilayered Ag nanoparticles SERS substrate (or other coinage metals) was prepared by a two-step electroless deposition of Ag on Ti substrate. This was achieved by in situ reduction of Ag precursor to subsequently form a Ag nanoflake (Ag NF) layer and a Ag nanoparticle (Ag NPs) layer on the Ti base (Ti/AgNFs/AgNPs). The as-prepared SERS substrate showed a substantially enhanced SERS effect for small molecule detection and detection limit as low as 1.0 × 10^-17 M for picric acid (PA), 1.0 × 10^-14 M for p-nitrotoluene (PNT) and 1.0 × 10^-6 M for uric acid (UA) were obtained respectively. The facile method developed in this work should be widely applicable for in-situ preparation of other SERs substrates.

Flexible 2D nanocellulose-based SERS substrate for pesticide residue detection

Nanocellulose holds considerable promise as an effective surface-enhanced Raman scattering (SERS) substrate for sensitive detection of trace targets. Flexible and high-sensitivity two-dimensional (2D) SERS substrates based on nanocrystalline cellulose (CNC) film were successfully developed via self assembly of two plasma nanoparticles: gold nanoflowers (AuNFs) and silver-coated gold nanocubes (Au@AgNCs). The loading process allows the precise control of nanoparticle distribution density and uniformity on CNC film, which are closely related to the plasma coupling effect between particles. The obtained CNC/Au@AgNC flexible two-dimensional substrate could sensitively detect pesticide residues on apple surface, and the detection limits (LOD) of dimethoate and acetamiprid were 4.1 and 10.7 μg/L, respectively. In addition, Raman signal intensity showed a good linear relationship with pesticide concentration in the range of 10-100 μg/L, which provided great potential for high sensitivity and field detection of dangerous targets.

Emerging trends in point-of-care sensors for illicit drugs analysis

Consumption of illicit narcotic drugs and fatal or criminal activities under their influence has become an utmost concern worldwide. These drugs influence an individual's feelings, perceptions, and emotions by altering the state of consciousness and thus can result in serious safety breaches at critical workplaces. Point-of-care drug-testing devices have become the need-of-the-hour for many sections such as the law enforcement agencies, the workplaces, etc. for safety and security. This review focuses on the recent progress on various electrochemical and optical nanosensors developed for the analysis of the most common illicit drugs (or their metabolites) such as tetrahydrocannabinol (THC), cocaine (COC), opioids (OPs), amphetamines & methamphetamine, and benzodiazepine (BZDs). The paper also highlights the sensitivity and selectivity of various sensing modalities along with evolving parameters such as real-time monitoring and measurement via a smart user interface. An overall outlook of recent technological advances in point of care (POC) devices and guided insights and directions for future research is presented.

Sandwich optoplasmonic hybrid structure for surface enhanced Raman spectroscopy

Combined with photonic microstructure and plasmonic nanostructure, the optoplasmonic hybrid structure with fantastic optical properties attracts lots of attentions in recent years. With the help of light enrichment by dielectric photonic microenvironment, the embedded plasmonic nanoantennas generate much greater electromagnetic field enhancement at surface for light harvesting compared to conventional plasmonic nanostructures. In this work, a sandwich optoplasmonic hybrid structure is developed for surface enhanced Raman spectroscopy (SERS) detection, which is consisted of polymethyl methacrylate (PMMA) microspheres array, self-assembled Ag nanoparticles (AgNPs) film and SiO₂ microsphere (PMMA@AgNPs@SiO₂). The SERS spectra collected on this optoplasmonic substrate point out it has high sensitivity with limit of detection (LOD) at 10 fM. The experimental data demonstrate both the PMMA microarray and SiO₂ microsphere play important roles in enrichment of light illuminating at AgNPs for SERS detection, which is confirmed by the simulated electric field distributions. This sandwich optoplasmonic hybrid structure not only enlarges research field of surface plasmon, but also provides a novel SERS subtract for sensitive analysis in chem/bio-field.

Contactless and robust dielectric microspheres-assisted surface-enhanced Raman scattering sensitivity improvement for anthrax biomarker detection

This report presents a contactless and robust dielectric microspheres (DMs)-assisted surface enhanced Raman scattering (SERS) enhancement method to improve SERS detection sensitivity detection sensitivity. DMs that could focus and collect light were embedded within the polydimethylsiloxane (PDMS) film to avoid direct contact with the analytical solution and improve detection reliability. The as prepared DMs embedded PDMS DMs PD MS film was integrated with a microfluidic technique to enhance the SERS signal of a liquid substrate. Detection in microfluidic systems can reduce reagent consumption, shorten assay time, and avoid evaporation of the colloid substrate solution. The robustness and potential influencing factors of DMs PDMS film assisted SERS enhancement (DERS) were evaluated using 4-aminothiophenol (4-ATP) as the Raman probe. The sensing performance of the proposed method toward dipicolinic acid (DPA) was evaluated, and an evident signal intensification was obtained. Remarkably, the DMs PDMS film can also be implemented on solid substrates. A proof-of-concept experiment was performed by covering the DMs PDMS film directly over an AgNPs@Si solid substrate wherein a 5.7-fold sensitivity improvement was achieved.

Photocatalytic Properties of Silver Nanospherical Arrays Driven by Surface Plasmons

Surface-enhanced Raman scattering (SERS) is a promising technique to study the plasma-driven photocatalytic reactions. Hemispherical alumina nanoarrays with a regular hexagonal arrangement are firstly prepared; then, silver hemispherical nanoarrays are synthesized on the surface of the arrays by silver evaporation. When a laser with a specific wavelength (633 nm) is irradiated on the silver nanoarrays, a large number of regularly arranged local surface plasmon enhancement regions (called “hot spots”) would be generated on its surface. After that, a layer of evenly distributed p-aminothiophenol (PATP) probe molecules was placed on the substrate and the photocatalytic reaction of PATP was driven by the local surface plasmon to form four 4′-di-mercaptoazobenzene (DMAB). Then, under the same experimental conditions, the later product was reversely reacted to form PATP molecule by the action of plasma in the presence of in situ sodium borohydride. SERS can be used to monitor the whole process of the photocatalytic reaction of PATP probe molecules driven by the plasma on the surface of the silver nanoarrays. This research achieves the drawing and erasing of molecular graphics in the micro- and nano-scales, as well as information encryption, reading, and erasing that have strong application value.

Plasma-Driven Photocatalysis Based on Gold Nanoporous Arrays

Various effects caused by surface plasmons including enhanced electromagnetic field, local heating, and excited electrons/holes can not only redistribute the electromagnetic field in the time domain and space but also redistribute the excited carriers and drive chemical reactions. In this study, firstly, an Au nanoporous array photocatalyst with the arrayed gauge was prepared by means of the anodic alumina template. Then, the formation of 4,4′-dimercaptoazobenzene (DMAB) by the surface plasmon-driven photocatalysis under 633 nm laser irradiation was investigated by means of Raman spectroscopy using aminothiophenol (PATP) as a probe molecule on gold nananoporous arrays. In addition, sodium borohydride was introduced in situ to realize the reverse photocatalytic reaction driven by the surface plasma. With the help of FDTD software, the plasma distribution characteristics on the surface of Au nanoporous arrays were simulated and analyzed. Through this practical method, it is expected to draw specific graphics, letters, and Chinese characters on the micro/nano scale, and realize the functions of graphics drawing, information encryption, reading, and erasing on the micro/nano scale.

Recent advances in developing optical and electrochemical sensors for analysis of methamphetamine: A review

Recognition of misused stimulant drugs has always been a hot topic from a medical and judicial perspective. Methamphetamine (MAMP) is an addictive and illegal drug that profoundly affects the central nervous system. Like other illicit drugs, the detection of MAMP in biological and street samples is vital for several organizations such as forensic medicine, anti-drug headquarters and diagnostic clinics. By emerging nanotechnology and exploiting nanomaterials in sensing applications, a great deal of attention has been given to the design of analytical sensors in MAMP tracing. For the first time, this study has briefly reviewed all the optical and electrochemical sensors in MAMP detection from earlier so far. How various receptors with engineering nanomaterials allow developing novel approaches to measure MAMP have been studied. Fundamental concepts related to optical and electrochemical recognition assays in which nanomaterials have been used and relevant MAMP sensing applications have been comprehensively covered. Challenges, opportunities and future outlooks of this field have also been discussed at the end.

Au nanobowtie on a SiO2 microsphere for optoplasmonic trapping

The combination of photonic and plasmonic elements with complementary optical properties has stimulated the development of optoplasmonic hybrid systems, in which photonic and plasmonic elements can interact synergistically, breaking through the limitations of traditional structures. In this paper, a new optoplasmonic tweezer is theoretically proposed by using the Au nanobowtie and SiO₂ microsphere. The finite-difference time-domain simulation is used to study the influence of the size of the SiO₂ microsphere and the SiO₂ hemisphere in polydimethylsiloxane on the optical potential well. The simulation results show that the electric field intensity of the structure is increased by 6 times compared with the Au nanobowtie structure, and the gradient force and the trapping potential are also significantly improved.

Microfluidic Transport of Hybrid Optoplasmonic Particles for Repeatable SERS Detection

For its ultrahigh sensitivity, the microfluidic system combined with surface-enhanced Raman spectroscopy (SERS) becomes one of the most interesting topics in integrated online monitoring related fields. In previous reports, the commonest surface plasmon-enhanced substrates in microfluidics consist of immobilized metal nanostructures on the channel surface to overcome the disturbance of Brownian motion. In this work, a hybrid optoplasmonic microfluidic conveyer is developed, in which the movable, highly ordered optoplasmonic particles are delivered to the detection spot for SERS detection. Here, the optoplasmonic particle is the SiO₂ microsphere with in situ photochemical reduced Ag nanoparticles on the surface. Because of the converged light at the SiO₂ microsphere surface, the SERS spectra collected at this optoplasmonic particle in the channel exhibit excellent performance, which is confirmed by the simulated electric field distribution. In addition, the experimental data also demonstrate that the quantitative analysis is achieved at 1 nM in this optoplasmonic microfluidic conveyer. Furthermore, the used optoplasmonic particle can be ejected from the microfluidic channel by modulating the velocity of injected fluid such that the new optoplasmonic particle will be delivered to the detection spot for repeatable SERS detection in the same channel. The dynamic process of optoplasmonic particle transport is investigated in this microconveyer, and the built theoretical model to predict the particle release is highly identical with the experimental data. These data point out that our hybrid optoplasmonic microfluidic conveyer has repeatable enhanced substrates with the high SERS sensitivity to overcome the cross-contamination of different target molecules in repeatable detection.

Optoplasmonic film for SERS

Combining plasmonic and photonic elements, optoplasmonic hybrid structure exhibits excellent optical properties beyond conventional plasmonic or photonic structures. In this work, the optoplasmonic film consists of SiO2 microsphere and Au film without any nanostructures is investigated. With the help of a microsphere, the intensity of surface enhanced Raman spectroscopy (SERS) on Au film is highly enhanced (~1000 times) compared to bare Au film. The simulated electromagnetic field points out the enhancement caused by the optical lens effect of SiO2 microsphere that high light intensity is generated under the microsphere to excite surface plasmon on Au film. Furthermore, our data demonstrates the microsphere lens enhancement is greatly influenced by the size of the SiO2 microsphere and wavelength of incident light. This interesting film with a simple configuration could overcome the challenges in the fabrication and store process induced by nanostructures, which play an important role in SERS application. Our work not only enlarges the knowledge of the optoplasmonic hybrid structure, but also exhibits excellent application prospective in light harvest field e.g. enhanced spectrum, photocatalysis, optothermal effect, and hot electron generation, etc.

SP, N. M, Barik AK, Pai KM, Unnikrishnan VK, George SD, Kartha VB, Chidangil S. Photonics of human saliva: potential optical methods for the screening of abnormal health conditions and infections

Human saliva can be treated as a pool of biological markers able to reflect on the state of personal health. Recent years have witnessed an increase in the use of optical devices for the analysis of body fluids. Several groups have carried out studies investigating the potential of saliva as a non-invasive and reliable clinical specimen for use in medical diagnostics. This brief review aims to highlight the optical technologies, mainly surface plasmon resonance (SPR), Raman, and Fourier transform infrared (FTIR) spectroscopy, which are being used for the probing of saliva for diverse biomedical applications. Advances in bio photonics offer the promise of unambiguous, objective and fast detection of abnormal health conditions and viral infections (such as COVID-19) from the analysis of saliva.

Automatic Sensing Setup for Methamphetamine Based on the Reactional Wettability Variation Strategy

An automatic setup for reactional wettability variation (RWV) was developed by interlinking liquid selection and transportation, object movement, and image recognition. In this way, the performance of the RWV strategy is updated to a nearly unmanned control manner with the example of methamphetamine and its aptamer. On the automatic RWV detection setup, the sensing surface acts similarly as before. The aptamer-based sensing surface resulted from the breakdown of the hydrophobic basis. The hydrophobicity is constructed on the metastable aptamer layer, which is responsive to the corresponding target. Methamphetamine interacts with its corresponding aptamer and destroys the basis of the hydrophobicity. A decrease in contact angle indicates the existence of methamphetamine. The RWV phenomenon is also affected by concentration and temperature. The development of an automatic detection ability would bring new possibilities to the surface reaction on smarter detection.