Mirrorlike Plasmonic Capsules for Online Microfluidic Raman Analysis of Drug in Human Saliva and Urine

Design and engineering of 3D plasmonic superstructure based on Pickering emulsion templates for surface-enhanced Raman spectroscopy applications in chemical and biomedical sensing

The integration of Pickering emulsion as a versatile template facilitates the assembly of nanoscale and microscale NPs, leading to the formation of intricate 3D superstructures. These superstructures exhibit collective properties, including optical, electric, and catalytic functionalities, surpassing individual building block. This review comprehensively explores the design and engineering principles behind the creation of these multifaceted superstructures. The exploration begins with the fundamental aspects of surface chemistry governing nanoparticles, a crucial factor in directing their assembly behavior at the curved liquid-liquid emulsion interface. Emphasis is placed on understanding emulsion stability, a pivotal element guiding the formation of stable 3D architectures. The discussion extends to unraveling the underlying mechanisms promoting the formation of these 3D superstructures. The focus lies in elucidating the optical functionalities of these superstructures, particularly in the context of surface-enhanced Raman spectroscopy application. The surveyed literature showcases diverse Pickering emulsion-based strategies employed in the assembly of plasmonic nanoparticles into intricate superstructures, offering controlled architectures and unlocking unique potentials for chemical and biochemical sensing.

Saliva Analysis Based on Microfluidics: Focusing the Wide Spectrum of Target Analyte

Saliva is one of the most critical human body fluids that can reflect the state of the human body. The detection of saliva is of great significance for disease diagnosis and health monitoring. Microfluidics, characterized by microscale size and high integration, is an ideal platform for the development of rapid and low-cost disease diagnostic techniques and devices. Microfluidic-based saliva testing methods have aroused considerable interest due to the increasing need for noninvasive testing and frequent or long-term testing. This review briefly described the significance of saliva analysis and generally classified the targets in saliva detection into pathogenic microorganisms, inorganic substances, and organic substances. By using this classification as a benchmark, the state-of-the-art research results on microfluidic detection of various substances in saliva were summarized. This work also put forward the challenges and future development directions of microfluidic detection methods for saliva.

Strong π-Metal Interaction Enables Liquid Interfacial Nanoarray-Molecule Co-assembly for Raman Sensing of Ultratrace Fentanyl Doped in Heroin, Ketamine, Morphine, and Real Urine

Toward the challenge on reliable determination of trace fentanyl to avoid opioid overdose death in drug crisis, here we realize rapid and direct detection of trace fentanyl in real human urine without pretreatment by a portable surface enhanced Raman spectroscopy (SERS) strategy on liquid/liquid interfacial (LLI) plasmonic arrays. It was observed that fentanyl could interact with the gold nanoparticles (GNPs) surface, facilitate the LLI self-assembly, and consequently amplify the detection sensitivity with a limit of detection (LOD) as low as 1 ng/mL in aqueous solution and 50 ng/mL spiked in urine. Furthermore, we achieve multiplex blind sample recognition and classification of ultratrace fentanyl doped in other illegal drugs, which has extremely low LODs at mass concentrations of 0.02% (2 ng in 10 μg of heroin), 0.02% (2 ng in 10 μg of ketamine), and 0.1% (10 ng in 10 μg of morphine). A logic circuit of the AND gate was constructed for automatic recognition of illegal drugs with or without fentanyl doping. The data-driven analog soft independent modeling model could quickly distinguish fentanyl-doped samples from illegal drugs with 100% specificity. Molecular dynamics (MD) simulation elucidates the underlying molecular mechanism of nanoarray-molecule co-assembly through strong π-metal interactions and the differences in the SERS signal of various drug molecules. It paves a rapid identification, quantification, and classification strategy for trace fentanyl analysis, indicating broad application prospects in response to the opioid epidemic crisis.

Capillary-force-assisted self-assembly of gold nanoparticles into highly ordered plasmonic thin films for ultrasensitive SERS

In this study, a capillary device based on the surface plasmon-enhanced Raman scattering effect was prepared by a simple and easy method. First, the capillary was treated with APTES solution. Due to the electrostatic effect, gold nanoparticles could be easily and tightly assembled in the capillary inner wall. On this basis, the effects of changing the concentration of APTES, the concentration of colloids and the soaking time of the capillary in the colloids on the assembly of gold nanoparticles on the inner wall of the capillary were studied, and the SERS enhancement effect under different conditions was analyzed, and the optimal solution was successfully found. At the same time, the reason why the capillary substrate shows better SERS performance than the traditional planar substrate is deeply discussed. Since the nanoparticles can be attached to the upper and lower surfaces of the inner wall of the capillary, the utilization rate of nanoparticles and laser is improved, thereby achieving higher enhancement. For the detection of the probe molecule rhodamine 6G, it was proved that the substrate has good uniformity and the lowest detection limit can reach 10^-10 M. Finally, the real-life pesticide thiram and the food additive aspartame were tested, and the detection limits could reach 10^-6 M and 0.25 g L^-1. It is confirmed that the prepared capillary shows excellent SERS performance and can be used for rapid detection in various fields.

Microfluidic nanodevices for drug sensing and screening applications

The outbreak of pandemics (e.g., severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 in 2019), influenza A viruses (H1N1 in 2009), etc.), and worldwide spike in the aging population have created unprecedented urgency for developing new drugs to improve disease treatment. As a result, extensive efforts have been made to design novel techniques for efficient drug monitoring and screening, which form the backbone of drug development. Compared to traditional techniques, microfluidics-based platforms have emerged as promising alternatives for high-throughput drug screening due to their inherent miniaturization characteristics, low sample consumption, integration, and compatibility with diverse analytical strategies. Moreover, the microfluidic-based models utilizing human cells to produce in-vitro biomimetics of the human body pave new ways to predict more accurate drug effects in humans. This review provides a comprehensive summary of different microfluidics-based drug sensing and screening strategies and briefly discusses their advantages. Most importantly, an in-depth outlook of the commonly used detection techniques integrated with microfluidic chips for highly sensitive drug screening is provided. Then, the influence of critical parameters such as sensing materials and microfluidic platform geometries on screening performance is summarized. This review also outlines the recent applications of microfluidic approaches for screening therapeutic and illicit drugs. Moreover, the current challenges and the future perspective of this research field is elaborately highlighted, which we believe will contribute immensely towards significant achievements in all aspects of drug development.

Multi-analyte High-Throughput Microplate-SERS Reader with Controllable Liquid Interfacial Arrays

High-throughput surface-enhanced Raman scattering (SERS) reader, especially for liquid sample testing, is of great significance and huge demand in biology, environment, and other analytical fields. Inspired by the principle of microplate reader, herein, we developed a microplate-SERS reader for semiautomatic and high-throughput assays by virtue of three-dimensional liquid interfacial arrays (LIAs). For the first time, the formation of LIA in oil-in-water state, water-in-oil state, and two-dimensional plane state is realized by operating the hydrophilicity (contact angle) of the container. Through the force analysis of LIA, the effect of organic (O) phase density on the relative position of LIA was quantified. In addition, the optimized reader offers fast and continuous semiautomatic detection of 12 samples below 10 min with great signal reproducibility (calibration with the characteristic peak of O phase as the internal standard). The isolated wells in the microplate prevent analyte cross talk, allowing accurate quantification of each sample. Multiplex analysis capability highlights that this reader has the ability of rapid identification and quantification of samples containing various analytes and concentrations. The results demonstrate high-resolution dual and triple analyte detection with fully preserved signal and Raman features of individual analytes in a mixture, which implies that it also has excellent anticounterfeiting applications. This microplate-SERS reader combines the superior advantages of the LIA, microplate, and SERS techniques to retrieve the molecular vibrational fingerprints of various chemicals in complex media.

Advances in droplet microfluidics for SERS and Raman analysis

Raman spectroscopy can realize qualitative and quantitative characterization, and surface-enhanced Raman spectroscopy (SERS) can further enhance its detection sensitivity. In combination with droplet microfluidics, some significant but insurmountable limitations of SERS and Raman spectroscopy can be overcome to some extent, thus improving their detection capability and extending their application. During the past decade, these systems have constantly developed and demonstrated a great potential in more applications, but there is no new review systematically summarizing the droplet microfluidics-based Raman and SERS analysis system since the first related review was published in 2011. Thus, there is a great need for a new review to summarize the advances. In this review, we focus on droplet microfluidics-based Raman and SERS analysis, and summarize two mainstream research directions on this topic up to now. The one is SERS or Raman detection in the moving droplet microreactors, including analysis of molecules, single cells and chemical reaction processes. The other one is SERS active microparticle fabrication via microfluidic droplet templates covering polymer matrix and photonic crystal microparticles. We also comment on the advantages, disadvantage and correlation resolution of droplet microfluidics for SERS or Raman. Finally, we summarize these systems and illustrate our perspectives for future research directions in this field.

Effect of Methadone and Tramadol Opioids on Stem Cells Based on Integrated Plasmonic-Ellipsometry Technique

Introduction: Plasmonic biosensors provide high sensitivity in detecting the low amount of biomarkers and pharmaceutical drugs. We studied the mesenchyme cell activity under the treatment of common sedative drugs of methadone and tramadol using the integrated plasmonic-ellipsometry technique. Methods: Mesenchymal stem cells were cultured on patterned plasmonic chips under the treatment of methadone and tramadol drugs. Three cultured chips were kept non-treated as the control ones. The plasmonic-ellipsometry technique was applied to study the signaling characteristic of the cells affected by these two drugs. In this technique, optical information regarding the amplitude ratio and phase change between p- and s-polarized light was recorded. Results: This drug treatment could affect the spectral plasmonic resonance and subsequently the phase shift (Δ) and the amplitude ratio (Ψ) values under p- and s-polarized impinging light. A more significant Δ value for tramadol treatment meant that the phase split was larger between p- and s-polarized light. Tramadol also had more prominent absolute Δ eff and Ψ eff values in comparison with methadone. Conclusion: We showed that tramadol caused more contrast in phase shift (Δ) and amplitude ratio (Ψ) between p- and s-polarized impinging light for cultured stem cells in comparison with methadone. It means that tramadol differentiated more the optical responses for p- and s-polarized lights compared to methadone. Our proposed technique possesses the potential of quantitative and qualitative analysis of drugs on humans even on a cell scale.

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.

Quantitative determination of peroxide value of edible oil by algorithm-assisted liquid interfacial surface enhanced Raman spectroscopy

Edible oil is an indispensable food in daily life but early detection of its lipid oxidation is difficult. Developing new, rapid and accurate screening technique is urgently needed for oil quality control. Here we developed a surface-enhanced Raman spectroscopy analyzer based on plasmonic metal liquid-like platform (PML-SERS), which could directly analyze the oil sample in ca. 3 min. This analyzer has the ability and sensitivity to identify fingerprint peak changes. Moreover, the relative Raman intensity, I_1265/1436, has a good correlation with peroxide value (POV), which is used for quantitative detection. The fitting model combined with principal component analysis (PCA) realized rapid spectral recognition for determining POV in edible oil oxidation. The relative deviation between the POV measured by PML-SERS and the national standard method (NSM) was less than 10%. Our platform provided a practical solution for ultra-sensitive and fast analysis of POV in oil oxidation.

A dual-functional PDMS-assisted paper-based SERS platform for the reliable detection of thiram residue both on fruit surfaces and in juice

In this work, a dual-functional SERS platform was developed via a paper-based SERS substrate with the aid of hydrophobic polydimethylsiloxane (PDMS) for effective and reliable measurements of thiram on fruit surfaces and in juice. Specifically, the paper-based SERS substrate was fabricated by coating with a core-shell Au@Ag nanorod monolayer, and the SERS performance was optimized compared with multilayer adsorption. Moreover, a versatile SERS platform was constructed by simply pasting the paper-based substrate in reverse onto PDMS using polymethyl methacrylate (PMMA) tape. On the one hand, this detection platform was able to realize sample enrichment due to the excellent hydrophobicity of PDMS, thereby increasing the sensitivity of measurements, and its function was successfully displayed through the identification of thiram in orange juice. On the other hand, PDMS could also play a supporting role and the paper-based substrate reversely stuck on PDMS was able to extract samples on the side without nanoparticles, which greatly avoids damage to nanoparticles on the substrate. Therefore, the accuracy of analysis was significantly improved and the inspection of thiram on the surface of an orange was demonstrated based on this function. As a result, this proposed SERS platform provides a new strategy for preparing multifunctional SERS sensors for the on-site monitoring of chemical contaminants in the food-safety field.

Lab-On-Capillary Platform for On-Site Quantitative SERS Analysis of Surface Contaminants Based on Au@4-MBA@Ag Core-Shell Nanorods

A portable and highly reproducible lab-on-capillary surface-enhanced Raman scattering (SERS) platform was developed using a specially designed homemade device for rapid on-site SERS measurement. In particular, this platform was composed of a capillary with a tiny orifice, which allows an effective and lossless sample extraction, resulting in high SERS performance. The capillary-based plasmonic substrate was prepared by compactly assembling Au@Ag core-shell nanorods (NRs) embedded with the 4-mercaptobenzoic acid (4-MBA) molecule as an internal standard onto the inner wall of a capillary tube. The fabrication process is facile and convenient with no requirement for complicated procedures. The exclusively prepared nanoparticles were able to significantly improve the signal consistency and overcome the limitations of reliable quantitative SERS analysis compared with conventional methods. Importantly, it was found that this capillary-based substrate with higher sensitivity was essentially attributed to more valid nanoparticles in the effective laser excitation region derived from the unique structure of the capillary. Furthermore, the applicability of the Au@4-MBA@Ag nanorod-decorated capillary for the quantitative identification of fungicides (malachite green and crystal violet) on the shell was demonstrated. As a result, this proposed lab-on-capillary sensor holds promising practical potential for rapid on-site analysis, especially for various contaminants on an uneven surface.

Breaking the Affinity Limit with Dual-Phase-Accessible Hotspot for Ultrahigh Raman Scattering of Nonadsorptive Molecules

For surface-enhanced Raman scattering (SERS) analysis, only analytes that can be absorbed spontaneously onto a noble metal surface can be detected effectively. Therefore, getting nonadsorptive molecules close enough to the surface has always been a key challenge in SERS analysis. Here absorbance measurements show that the liquid-interfacial array (LIA) does not adsorb or enrich benzopyrene (Bap) molecules, which lack effective functional groups that can interact with the noble metal surfaces. But the SERS intensity of 0.1 ppm Bap on the LIA is 10 times larger than that of 10 ppm Bap on traditional solid substrate, i.e., 3 orders of magnitude of enhancement. The LIA overcomes the restriction of affinity between Bap molecules and the metal surface, and the Bap molecules can easily enter nanogaps without steric hindrance. Furthermore, both adsorptive and nonadsorptive molecules were used to observe the SERS enhancement behavior on the LIA platforms. In multiple detection, competitive SERS signal changes could be observed between adsorptive and nonadsorptive molecules or between nonadsorptive and nonadsorptive molecules. A theoretical scheme was profiled for localized surface plasmon resonance (SPR) properties of the LIA. Finite difference-time domain (FDTD) simulation shows that the LIAs have biphasic and accessible asymmetric hotspots, and the electric field enhancement in the CHCl₃ (O) phase is approximately four times larger than that of the water (W) phase. In addition, the position and relative strength of the electromagnetic field depend on the spatial position of gold nanoparticles (GNPs) relative to the liquid-liquid interface (LLI), i.e., when the GNP dimer is completely immersed in a certain phase, the electromagnetic field enhancement of the CHCl₃ phase is approximately 7 times larger than that of the W phase. We speculate that dual-phase-accessible hotspots and the hydrophobic environment provided by CHCl₃ are two important factors contributing to successful detection of four common polycyclic aromatic hydrocarbons (PAHs) with a detection limit of 10 ppb. Finally, the LIA platform successfully realizes simultaneous detection of multiple PAHs in both plant and animal oils with good stability. This study provides a new direction for the development of high-efficiency and practical SERS technology for nonadsorptive molecules.