Antipsychotic drug poisoning monitoring of clozapine in urine by using coffee ring effect based surface-enhanced Raman spectroscopy

Development of a Low-Cost Paper-Based Platform for Coffee Ring-Assisted SERS

The need for highly sensitive, low-cost, and timely diagnostic technologies at the point of care is increasing. Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopic technique that is an advantageous technique to address this need, as it can rapidly detect analytes in small or dilute samples with improved sensitivity compared to conventional Raman spectroscopy. Despite the many advantages of SERS, one drawback of the technique is poor reproducibility due to variable interactions between nanoparticles and target analytes. To overcome this limitation, coupling SERS with the coffee ring effect has been implemented to concentrate and localize analyte-nanoparticle conjugates for improved signal reproducibility. However, current coffee ring platforms require laborious fabrication steps. Herein, we present a low-cost, two-step fabrication process for coffee ring-assisted SERS, utilizing wax-printed nitrocellulose paper. The platform was designed to produce a highly hydrophobic paper substrate that supports the coffee ring effect and tested using gold nanoparticles for SERS sensing. The nanoparticle concentration and solvent were varied to determine the effect of solution composition on ring formation and center clearance. The SERS signal was validated using 4-mercaptobenzoic acid (MBA) and tested with Moraxella catarrhalis bacteria to ensure functionality for chemical and biological applications. The limit of detection using MBA is 41.56 nM, and the biochemical components of the bacterial cell wall were enhanced with low spectral variability. The developed platform is advantageous due to ease of fabrication and use, representing the next step toward implementing low-cost coffee ring-assisted SERS for point-of-care sensing.

Single versus Double Coffee-Ring Effect Patterns in Thin-Layer Chromatography Coupled with Surface-Enhanced Raman Spectroscopic Analysis of Anti-Diabetic Drugs Adulterated in Herbal Products

In thin-layer chromatography coupled with surface-enhanced Raman spectroscopy (TLC-SERS), the coffee ring effect (CRE) describes the formation of a ring-shape spot (blank in the middle and darker on the edge) caused by the aggregation of silver nanoparticles (Ag NPs), alone (single CRE) or with the analytes (double CRE). In this work, the SCRE and DCRE were investigated in two anti-diabetic drugs, hydrophobic glibenclamide (GLB) and more hydrophilic metformin (MET). The SCRE occurred in GLB analysis, as opposed to the DCRE that occurred in MET. It was proven that for optimization of the TLC-SERS analytical procedure, it is necessary to distinguish the CRE patterns of analytes. Additionally, MET and GLB were analyzed with the developed TLC-SERS method and confirmed by another validated method using high-performance liquid chromatography. Four herbal products collected on the market were found to be adulterated with GLB or/and MET; among those, one product was adulterated with both MET and GLB, and two products were adulterated with GLB at a higher concentration than the usual GLB prescription dose. The TLC-SERS method provided a useful tool for the simultaneous detection of adulterated anti-diabetic herbal products, and the comparison of the SCRE and DCRE provided more evidence to predict CRE patterns in TLC-SERS.

Simultaneous quantification of serum albumin and gamma globulin using Zn(II)-metallosurfactant via a coffee ring pattern

Herein, we report interactivity and conjugate formation ability between a Zn(II)-metallosurfactant and two clinically relevant serum proteins, albumin (ALB) and γ-globulin (GGB). We found that the surfactant-ALB conjugate promotes coffee ring formation, whereas with GGB it gets suppressed, which is due to the difference in structural anisotropy and hydrophobicity of the conjugates. Additionally, validation of this biosensing platform has been established in human serum samples, and it has potential applications for on-spot rapid diagnostics in remote areas.

Cyclodextrin-assisted SERS determination of fluoroquinolone antibiotics in urine and blood plasma

This paper describes the use of cyclodextrins (CDs) to improve the determination of fluoroquinolone antibiotics in human body fluids using surface-enhanced Raman spectroscopy (SERS). CDs were used to (i) prepare the CD-SERS substrate (synthesis and stabilization of silver nanoparticles), (ii) increase the sensitivity of the assay by enhancing the interaction between analyte molecules and the substrate, and (iii) improve the analysis accuracy by reducing the interaction between the substrate and endogenous components of body fluids. Two native CDs (α-CD and β-CD) and two of their derivatives with hydroxypropyl groups were tested, and the best results were obtained with CD-SERS substrate prepared using native β-CD. The CD-SERS assay has been developed and optimized for the determination of commonly used and structurally related fluoroquinolones (ciprofloxacin, norfloxacin, pefloxacin, and levofloxacin) in urine and blood plasma samples. Importantly, the non-significant difference in the interaction of the CD-modified SERS substrate with various fluoroquinolones has been successfully used to develop a versatile assay suitable for the analyte-class-specific analysis. Calibration plots were obtained for concentration ranges suitable for the determination of the antibiotics in urine (50-500 μg mL^-1) and blood plasma (1-6 μg mL^-1). The following figures of merit were obtained (for urine and blood plasma, respectively): RSD values are ≤15% and ≤23%, LOD values are 2.9-5.8 and 0.05-0.34 μg mL^-1, recovery ranges are 96-105% and 91-111%. In addition, the influence of excessive concentrations of some main endogenous components of the body fluids on the analytical signal was studied. This step was used to evaluate possible limitations of the assay associated with the deviation of the composition of the body fluid matrix. Therefore, accounting for the short analysis time (≤15 min) and the use of a portable Raman spectrometer, the proposed assay can be suggested for therapeutic drug monitoring in hospitals.

A Rapid Therapeutic Drug Monitoring Strategy of Carbamazepine in Serum by Using Coffee-Ring Effect Assisted Surface-Enhanced Raman Spectroscopy

Carbamazepine (CBZ) has a narrow therapeutic concentration range, and therapeutic drug monitoring (TDM) is necessary for its safe and effective individualized medication. This study aims to develop a procedure for CBZ detection in serum using coffee-ring effect assisted surface-enhanced Raman spectroscopy (SERS). Silver nanoparticles deposited onto silicon wafers were used as the SERS-active material. Surface treatment optimization of the silicon wafers and the liquid-liquid extraction method were conducted to eliminate the influence of impurities on the silicon wafer surface and the protein matrix. The proposed detection procedure allows for the fast determination of CBZ in artificially spiked serum samples within a concentration range of 2.5-40 μg·mL^-1, which matches the range of the drug concentrations in the serum after oral medication. The limit of detection for CBZ was found to be 0.01 μg·mL^-1. The developed method allowed CBZ and its metabolites to be ultimately distinguished from real serum samples. The developed method is anticipated to be a potential tool for monitoring other drug concentrations.

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.

Human metabolite detection by surface-enhanced Raman spectroscopy

Metabolites are important biomarkers in human body fluids, conveying direct information of cellular activities and physical conditions. Metabolite detection has long been a research hotspot in the field of biology and medicine. Surface-enhanced Raman spectroscopy (SERS), based on the molecular “fingerprint” of Raman spectrum and the enormous signal enhancement (down to a single-molecule level) by plasmonic nanomaterials, has proven to be a novel and powerful tool for metabolite detection. SERS provides favorable properties such as ultra-sensitive, label-free, rapid, specific, and non-destructive detection processes. In this review, we summarized the progress in recent 10 years on SERS-based sensing of endogenous metabolites at the cellular level, in tissues, and in biofluids, as well as drug metabolites in biofluids. We made detailed discussions on the challenges and optimization methods of SERS technique in metabolite detection. The combination of SERS with modern biomedical technology were also anticipated.

Cyclodextrin-assisted surface-enhanced Raman spectroscopy: a critical review

Numerous approaches have been proposed to overcome the intrinsically low selectivity of surface-enhanced Raman spectroscopy (SERS), and the modification of SERS substrates with diverse recognition molecules is one of such approaches. In contrast to the use of antibodies, aptamers, and molecularly imprinted polymers, application of cyclodextrins (CDs) is still developing with less than 100 papers since 1993. Therefore, the main goal of this review is the critical analysis of all available papers on the use of CDs in SERS analysis, including physicochemical studies of CD complexation and the effect of CD presence on the Raman enhancement. The results of the review reveal that there is controversial information about CD efficiency and further experimental investigations have to be done in order to estimate the real potential of CDs in SERS-based analysis.

Ethanol-extraction SERS strategy for highly sensitive detection of poisons in oily matrix

The sensitive detection and identification of toxicants in oily matrices have suffered from difficulty in poisoning incidents, therefore it is necessary to develop the rapid and efficient analytical method to realize the on-site screening and analyzing. In this report, the surface-enhanced Raman spectroscopy (SERS) method was used to detect paraquat and diquat poisons in various oily matrix coupled with solvent extraction. The solvent extraction not only remove interfering impurities of oily substrates, but also can enrich and separate the poisons from oily matrix. It was demonstrated that the ethanol as the extractant was suitable for the rapid separation of poisons such as paraquat (PQ) and diquat (DQ) in oily matrix (soy sauce, pasta sauce, sesame oil, chili oil). Moreover, combined with a handheld Raman spectrometer, the entire detection process was completed within 8 min with the level of 10 ppb PQ and 100 ppb DQ. Furthermore, double-blind experiments verify the reliability of this method. The results demonstrate that this rapid and convenient method could be used for the effective enrichment and sensitive detection of poisons in several oily matrix and has the grate potential application in emergency response and public safety.

Optical biosensors - Illuminating the path to personalized drug dosing

Optical biosensors are low-cost, sensitive and portable devices that are poised to revolutionize the medical industry. Healthcare monitoring has already been transformed by such devices, with notable recent applications including heart rate monitoring in smartwatches and COVID-19 lateral flow diagnostic test kits. The commercial success and impact of existing optical sensors has galvanized research in expanding its application in numerous disciplines. Drug detection and monitoring seeks to benefit from the fast-approaching wave of optical biosensors, with diverse applications ranging from illicit drug testing, clinical trials, monitoring in advanced drug delivery systems and personalized drug dosing. The latter has the potential to significantly improve patients' lives by minimizing toxicity and maximizing efficacy. To achieve this, the patient's serum drug levels must be frequently measured. Yet, the current method of obtaining such information, namely therapeutic drug monitoring (TDM), is not routinely practiced as it is invasive, expensive, time-consuming and skilled labor-intensive. Certainly, optical sensors possess the capabilities to challenge this convention. This review explores the current state of optical biosensors in personalized dosing with special emphasis on TDM, and provides an appraisal on recent strategies. The strengths and challenges of optical biosensors are critically evaluated, before concluding with perspectives on the future direction of these sensors.

Paper-based SERS substrate and one-class classifier to monitor thiabendazole residual levels in extracts of mango peels

The assessment of pesticide residue levels demands fast, low cost and easy-to-use procedures which are not found in conventional methods. In this work, SERS substrates based on the deposition of gold nanoparticles (GNPs) on common office paper were prepared using a wax printer. These substrates combined with Data Driven Soft Independent Modelling of Class Analogies (DD-SIMCA), a one-class classifier algorithm, were used for detection of pesticide residues in water extracts of mango peels. Paper-based substrates made sample collection easier compared with conventional SERS methods, since few microliters of the pesticide aqueous extract from fruit peels needed to be deposited onto the substrate. Moreover, one-class classifiers dismiss the need for quantification or calibration curves. Classification of a fruit with residue levels in accordance to regulatory bodies' limits is based on a mathematical threshold. Just as in an authentication problem, all the possibilities for a given analysed fruit are now restricted to agreeing or not agreeing with current regulations. The performance of the one-class model was demonstrated by detecting thiabendazole (TBZ) residues at various mango samples, with all results being confirmed by HPLC-DAD analysis. The final model could distinguish samples with TBZ levels above the ones allowed by the Brazilian Health Regulatory Agency with 94% of selectivity and 92% of sensitivity, even in the presence of other pesticides.

Factors of Importance for Arsenic Migration/Separation under Coffee-Ring Effect on Silver Nanofilms

Surface-enhanced Raman spectroscopy (SERS) has been recognized as a promising analytical technique owing to its merit of nondestructive and fast detection capabilities. However, SERS usually suffers signal interferences from different analytes or a complicated matrix. Separation is an effective approach to solve the signal interference in the application of SERS. It was proposed that two concentric coffee rings could serve as a simple separation platform; however, there are still many questions to be answered for in-depth understanding. In this study, critical parameters during the formation of two concentric coffee rings are characterized for a better understanding of this phenomenon, including surface tension, surface morphology, and surface energy. Two arsenicals, including arsenate (As^V) and cacodylic acid (DMA^V), are chosen to study the arsenicals' separation/migration mechanism due to their significant difference in chemical properties. In the typical coffee ring, these two arsenicals have signal interference and only DMA^V is detected via SERS; however, they are detected along the radius of the two concentric coffee rings. The distribution of arsenicals on the two concentric coffee rings is further verified by the chromatographic method. Under this simple platform, interactions between the arsenicals and the surface of the silver nanofilm are pivotal to their migration/separation. By surface modification of silver nanofilm with small molecules, the surface polarity and surface ζ potential are manipulated. The signal dynamics of these two arsenicals are studied on these modified silver nanofilms. It is clear that the electrostatic interaction plays a more important role than the polarity in the arsenicals' migration. This study reveals the mechanism of small molecule migration/separation in the two concentric coffee rings and provides insights for future study of employing this simple platform.

Label-free diagnosis for colorectal cancer through coffee ring-assisted surface-enhanced Raman spectroscopy on blood serum

Surface-enhanced Raman spectroscopy (SERS) is garnering considerable attention for the swift diagnosis of pathogens and abnormal biological status, that is, cancers. In this work, a simple, fast and inexpensive optical sensing platform is developed by the design of SERS sampling and data analysis. The pretreatment of spectral measurement employed gold nanoparticle colloid mixing with the serum from patients with colorectal cancer (CRC). The droplet of particle-serum mixture formed coffee-ring-like region at the rim, providing strong and stable SERS profiles. The obtained spectra from cancer patients and healthy volunteers were analyzed by unsupervised principal component analysis (PCA) and supervised machine learning model, such as support-vector machine (SVM), respectively. The results demonstrate that the SVM model provides the superior performance in the classification of CRC diagnosis compared with PCA. In addition, the values of carcinoembryonic antigen from the blood samples were compiled with the corresponding SERS spectra for SVM calculation, yielding improved prediction results.

Arsenic Speciation on Silver Nanofilms by Surface-Enhanced Raman Spectroscopy

Surface-enhanced Raman spectroscopy (SERS), as a nondestructive and fast detection technique, is a promising alternative approach for arsenic detection, particularly for in situ applications. SERS-based speciation analysis according to the fingerprint SERS signals of different arsenicals has the potential to provide a superior technique in species preservation over the conventional chromatographic separation methods, albeit with some difficulties due to the similarity in SERS patterns. In this study, we explored a novel SERS method for arsenic speciation by using the separation potential of the coffee ring effect on negatively charged silver nanofilms (AgNFs). Four arsenic species, including arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MMA^V), and dimethylarsinic acid (DMA^V), were measured for fingerprint SERS signals in solution and on the films. Significant enhancement of SERS signals on the dried coffee ring stains by the AgNFs were observed except for As^III, and more importantly, arsenicals migrated varying distances during coffee ring development, promoting better speciation. Sodium dodecyl sulfate was then introduced into the droplet to reduce the droplet surface tension, facilitating the migration of solution into the peripheral region. Under the combined interactions of arsenicals with the AgNFs, solvent, and surfactant, enhanced separation between arsenicals was observed as a result of the formation of two concentric rings. Combining the SERS fingerprint signals and physical separation of arsenicals on the surface, arsenic speciation was achieved using the AgNFs substrate-based SERS technology, demonstrating the potential of the coffee ring effect for rapid separation and analysis of small molecules by SERS.

A fast response TLC-SERS substrate for on-site detection of hydrophilic and hydrophobic adulterants in botanical dietary supplements

Schematic illustration of TLC-SERS for detection of hydrophilic and hydrophobic adulterants in botanical dietary supplements.

In situ analysis of pesticide residues on the surface of agricultural products via surface-enhanced Raman spectroscopy using a flexible Au@Ag–PDMS substrate

In situ analysis of pesticide residues on the surface of agricultural products via surface-enhanced Raman spectroscopy using a flexible Au@Ag–PDMS substrate.

Polarization- and Angular-Resolved Optical Response of Molecules on Anisotropic Plasmonic Nanostructures

A sometimes overlooked degree of freedom in the design of many spectroscopic (mainly Raman) experiments involve the choice of experimental geometry and polarization arrangement used. Although these aspects usually play a rather minor role, their neglect may result in a misinterpretation of the experimental results. It is well known that polarization- and/or angular- resolved spectroscopic experiments allow one to classify the symmetry of the vibrations involved or the molecular orientation with respect to a smooth surface. However, very low detection limits in surface-enhancing spectroscopic techniques are often accompanied by a complete or partial loss of this detailed information. In this review, we will try to elucidate the extent to which this approach can be generalized for molecules adsorbed on plasmonic nanostructures. We will provide a detailed summary of the state-of-the-art experimental findings for a range of plasmonic platforms used in the last ~ 15 years. Possible implications on the design of plasmon-based molecular sensors for maximum signal enhancement will also be discussed.