BACKGROUND:A key restriction of label-free surface-enhanced Raman spectroscopy (SERS) in analysis of objects with complex composition (including with several target analytes) is the competition of mixture components for interaction with SERS-active surface. This leads to poor selectivity of the analysis of such mixtures (e.g., body fluids) and the need to use advanced sample pretreatment procedures such as HPLC or TLC. Therefore, this work aims to develop a set of simple and fast pretreatment steps (dilution, pH correction, etc.) to increase the sorption of the target analyte, reduce the sorption of admixtures, and prevent suppression of the target analyte SERS signal. RESULTS:We have developed label-free SERS assay suitable for the determination of three analytes (methotrexate, cephalosporin antibiotic, and creatinine) in one real urine sample as a model matrix with complex and deviating composition. The choice of drugs is justified by the need to monitor their concentration in urine during joint drug treatment of cancer patients with concomitant bacterial infection, while monitoring creatinine concentration helps to evaluate kidney function of the patients. Additionally, three cephalosporin representatives were used in the study to maximize versatility of the assay. As a results, the optimized pretreatment steps enable to eliminate the negative influence of excess of interferences (including other analytes) and achieve precise (≤12 % RSD) and accurate (88-111 % recovery) determination of several analytes in the therapeutically relevant ranges: 300-3000 μg mL-1 for creatinine, 20-200 μg mL-1 for methotrexate and cephalosporins. SIGNIFICANCE:Therefore, in addition to reporting a new SERS assay for the analysis of body fluids, this study clearly demonstrates the importance of taking into account competitive adsorption processes on the SERS substrate surface. We suggest making this practice mandatory when developing any label-free SERS assay because it enables to maximize the selectivity and accuracy of the analysis as well as to simplify the analysis procedure.

Analysis of real objects based on surface-enhanced Raman spectroscopy (SERS) often utilizes new SERS substrates and/or complex analysis procedures, and they are optimized for only the determination of a single analyte. Moreover, analysis simplicity and selectivity are often sacrificed for maximum (sometimes unnecessary) sensitivity. Consequently, this trend limits the versatility of SERS analysis and complicates its practical implementation. Thus, we have developed a universal, but simple SERS assay suitable for the determination of structurally related antibiotics (five representatives of the sulfanilamide class) in complex objects (human urine and saliva). The assay involves only mixing of acidified analyzed solution with co-activating agent (polydiallyldimethylammonium chloride - PDDA) and SERS substrate (standard colloidal silver nanoparticles). Acidification promotes the generation of SERS spectra with maximum similarity and intensity, which is explained by the favorable enhancement of the protonated sulfanilamide moiety (a structurally similar part of the studied antibiotics) as a result of its strong electrostatic interaction with the SERS-active surface. Meanwhile, the addition of PDDA improves analysis selectivity by reducing background signal from body fluids, enabling to simplify sample pretreatment (dilution for urine; mucin removal and dilution for saliva). Therefore, the assay allows for rapid (<= 10 min), precise, and accurate class-specific determination of sulfanilamides within concentration ranges suitable for non-invasive therapeutic drug monitoring in urine (40-600 mu M) and saliva (10-30 mu M). We also believe that thorough investigation of structurally related analytes and accompanying effects (e.g., high spectral similarity) is a promising direction to improve the understanding of SERS in general and expand its capabilities as an analytical tool.

Surface enhanced Raman spectroscopy (SERS) is meeting the requirements in biomedical science being a highly sensitive and specific analytical tool.

Surface-enhanced Raman spectroscopy (SERS) is a powerful biosensing technique that combines molecular fingerprint specificity with high sensitivity, detecting trace amounts using plasmonic-based metallic nanostructured sensor platforms. SERS strategies include direct and indirect, as well as targeted and untargeted methods, depending on sample complexity and target analyte affinity. The development of SERS platforms, such as microfluidic environments, lab-on-a-fiber approaches, and paper-based immunoassays, aims at creating portable systems for point-of-care use in clinical and non-lab settings. Combining SERS with other techniques enhances measurement conditions, miniaturization, and sensitivity. This review summarizes key analytical applications of SERS in biosensing, including medicine, clinical diagnostics, environmental monitoring, food quality assessment, and biological studies.

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 (alpha-CD and beta-CD) and two of their derivatives with hydroxypropyl groups were tested, and the best results were obtained with CD-SERS substrate prepared using native beta-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 suc- cessfully 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 mu g mL-1) and blood plasma (1-6 mu g 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 mu g 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.

Adaptation of medical treatment to a particular patient requires the monitoring the concentration of active substances or biomarkers in the body during medical treatment. When studying the individual therapeutic effect of chemotherapeutic drugs, fast simple methods for their determining are needed. It is especially important to control the concentration of cytostatics because of their high toxicity. The task of determining the concentration of cytostatics is important for biofluids and tissues, as well as for the design and validation of prolonged release systems, which are actively used and developed to reduce the toxic effect of cytostatics. However, the determination of such agents, especially anthracycline antibiotics, is complicated by their high propensity to absorption on biomolecules, forms variability, and sensitivity to media properties. This review critically considers existing methods for the determination of one of the anthracycline antibiotics, mitoxantrone (MTX), and the application of these methods for monitoring of MTX concentration.

The paper describes the use of native β-cyclodextrin (CD) for the modification of silver nanoparticles (AgNPs) in order to improve the determination of the anticancer drug methotrexate (MTX) using surface-enhanced Raman spectroscopy (SERS). A control experiment with unmodified AgNPs showed that the strong SERS signal of MTX can only be achieved in alkaline media. However, competitive interactions and the strong background signal of human body fluid components significantly challenge MTX determination in real samples. While previous reports propose the use of thorough sample pretreatment (e.g., solid phase extraction), the application of CD-modified AgNPs increases the SERS signal of MTX in neutral media by seven times which enables simplifying the analysis and improving its accuracy by reducing the influence of endogenous components of body fluids. A detailed study of the synthesis conditions (CD concentration and reaction time) and SERS registration conditions (pH, NaCl concentration, dilution of urine samples) was performed to maximize the analytical signal and signal-to-noise ratio. The final assay was tested for MTX determination in artificially spiked samples of real human urine. The results demonstrated that MTX can be determined within the concentration range suitable for therapeutic drug monitoring (20–300 μg mL−1) with satisfactory precision (6–15% RSD), accuracy (95–111% apparent recovery), and limit of detection (0.3 μg mL−1).

The work describes electrochemical (EC) protocol suitable for preparation of copper electrodes which can be used as substrates in surface-enhanced Raman spectroscopy (SERS). These SERS-active electrodes have been used for electrospectral studies based on the combination of electrochemical and SERS analysis (EC-SRS analysis). Several endogenous bodyfl uid components (urea, creatinine, uric acid, bilirubin) have been selected for the study because they can signifi cantly aff ect the SERS-based determination of other analytes in bodyfl uids (for example, drugs). The infl uence of the SERS-active electrode polarization (applied potential) and the pH level of the analyte solutions on the SERS signal and current value have been investigated. The polarization values corresponded to the maximum SERS signal are observed at negative values for all analytes (below −0.2 V vs. copper pseudo-reference electrode). The maximal SERS signal has been observed for most of the analytes in a neutral medium (at the optimum polarization value of the SERS-active electrode), and the weakest signal has been in an alkaline medium. The diminishing of EC-SERS signal at high pH values is explained by deprotonation of analyte molecules that deteriorates analyte adsorption onto the negatively polarized SERS-active electrodes. Analysis of the current-voltage curves has been used to estimate the possible infl uence of EC changes of the studied molecules on their EC-SERS signal. The results obtained in this work will be useful for the development of EC-SERS systems suitable for the determination of various endo- and exogenous compounds in human biofl uids.

Historically, electrochemical surface-enhanced Raman spectroscopy (EC-SERS) was the first format of SERS analysis; however, it is also the least frequently used SERS format for routine analysis. A key advantage of the EC-SERS analysis is the ability to regulate analyte adsorption-desorption by electrode polarization providing additional control over analytical signal and allowing for fast and easy fabrication, cleaning, and regeneration of SERS-active surface. Therefore, this review aims to collect the best ex-amples of analytical reports on the topic and analyze analytical performance of EC-SERS assays to highlight the problems that limit its practical application. The review discusses general design of EC-SERS setup and the factors influencing the potential of maximal SERS signal; standard and advanced formats of EC-SERS analysis; figures of merit, selectivity, critical limitations, and perspective directions. The analytically useful factors are discussed in more detail: specific physicochemical effects, "memory ef-fects" and reusability problems, side electrochemical reactions, and limited selectivity.(c) 2022 Elsevier B.V. All rights reserved.

The review is devoted to an analysis of the capabilities, limitations, and special features of the application of surface-enhanced Raman spectroscopy (SERS) to the determination of drugs and narcotics in human body fluids (blood, urine, and saliva). An analysis of the literature demonstrated that the most efforts of researchers were aimed at overcoming the main disadvantage of SERS as an analysis method-low selectivity, which is especially important in the case of complex objects such as biological fluids. In this regard, the main positive results in the SERS analysis of human biological fluids are currently associated with the development of procedures that minimize the level of a background signal. The procedures are based on various combinations of SERS with separation and preconcentration methods, the use of sample preparation, and the application of chemometrics to take into account the background component of an analytical signal. Significant progress is also associated with the development of multifunctional SERS-active materials, which make it possible to improve the selectivity of analysis. However, it is the analytical part of most works that is the weakest point, which requires further research, including the verification of SERS analysis procedures using control reference methods.

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.

The determination of antibiotic levels in body fluids is of great importance in the field of personalized medicine and therapeutic drug monitoring. We report on the determination of sulfamethoxazole (SMX), an antibacterial drug of the sulfanilamide class, in spiked human urine. The protocol is based on the combination of surface-enhanced Raman spectroscopy (SERS) and liquid-liquid extraction (LLE-SERS analysis). First, the urine was diluted to reduce its buffer properties and the influence of the intrinsic urine components on the background SERS signal. Second, the acidification of the diluted urine and SMX extracts was performed to facilitate SMX extraction by chloroform and suppress the background signal, respectively. Finally, the SMX determination process was performed using hydroxylamine-stabilized silver nanoparticles as the SERS substrate. The efficiency and reliability of the LLE-SERS analysis were studied using spiked urine samples obtained from healthy volunteers with an SMX content within the therapeutically relevant concentration range (10-200 mu g mL(-1)). Additionally, the verification of the analysis protocol was done using spiked urine samples obtained from oncology patients. The results of the verification demonstrate the applicability of the analysis for quantitative therapeutic drug monitoring due to the (i) strong suppression of the background SERS signal, which occurs as the result of LLE, dilution, and pH adjusting, (ii) satisfactory limit of detection of 1.7 mu g mL(-1), and (iii) simple, relatively fast (similar to 30 min), and cost-effective sample pretreatment. (C) 2020 Elsevier B.V. All rights reserved.

This report is dedicated to determination of anticancer drug methotrexate (MTX) in human urine using surface-enhanced Raman spectroscopy (SERS). Aluminum oxide loaded with silver nanoparticles (AO-Ag) was proposed as SERS-active sorbent and used for solid-phase extraction (SPE) of the analyte and its SERS-based determination (SPE-SERS protocol). MTX has strong SERS signal only in alkaline media that challenges its determination in urine due to strong background signal caused by creatinine. The application of SPE step enables to purify and concentrate the analyte making MTX determination possible. Also, the application of the same material for SPE pretreatment and SERS analysis enables to simplify and speed-up the protocol. The protocol was developed and tested using artificially spiked samples of human urine collected during different time of day to account deviating composition of the urine matrix. The use of dilution step of the analyte-containing urine was proposed prior SPE-SERS protocol to reduce the difference between morning-time- and daytime-collected urine achieving maximal reliability of the analysis. Additional physicochemical study was performed to estimate an influence of the primary intrinsic urine components (salts, urea, creatinine) and their mixtures on the analytical signal. Final protocol enables MTX determination in human urine within 20–300 μg mL−1 range of concentrations with satisfactory precision (11–19% RSD), accuracy (97–104% apparent recovery), and limit of detection (4.2 μg mL−1). Accounting that the analysis requires less than 15 min and portable Raman spectrometer, the protocol seems to be promising for therapeutic drug monitoring in hospitals to identify poor MTX clearance in a timely manner and minimize adverse effects of therapy.

The authors theoretically investigated absorbance spectra of the hypothetical 1D Cu clusters with 2–22 atoms and monoatomic thickness. In contrast to 3D isomers with interband transitions only (< 600 nm; intrinsic for any copper nanostructure), the 1D clusters possess strong absorbance bands within 650–1800 nm range depending on the cluster size (NIR bands). The band location in NIR range was explained by low binding number per copper atom that leads to weaker coupling of 4s electrons within the conduction band and reducing energy gap between vacant and occupied orbitals. The NIR bands are formed by HOMO → LUMO transitions and their large intensity was explained by highly hybridized sp character of HOMO and LUMO and by the low contribution of 3d electrons (< 10%). The analysis of the number of electrons involved to the formation of NIR bands demonstrates their prominent plasmonic (collective) character. For example, the NIR band of the cluster with 20 atoms (1636 nm) is formed by excitation of 5 electrons. In contrast, 0.35 and 0.44 electrons were involved to the formation of all absorbance bands within visible–NIR range (400–1000 nm) for spherical and tetrahedral 3D isomers, respectively. The results are in qualitative agreement with experimental results for copper nanorods and nanowires which also possess strong bands in the red–NIR range (> 600 nm) compared to the nanoparticles with spherical geometry. Additionally, the large clusters (16–22 atoms) possess multiple bands in NIR range that is also in agreement with the experiment.

Copper nanoparticles (CuNPs) were prepared through a wet chemistry method to be used as substituents for noble-metal-based materials in the determination of cephalosporin antibiotics in urine using surface-enhanced Raman spectroscopy (SERS). The synthesis of the CuNPs was optimized to maximize the analytical signal, and microwave heating was used to increase the reaction rate and improve the homogeneity of the CuNPs. Ceftriaxone (CTR), cefazolin (CZL), and cefoperazone (CPR) were used as the analytes of interest. The determination tests were performed on artificially spiked samples of real human urine with concentrations corresponding to therapeutic drug monitoring (TDM) (50-500 mu g mL(-1)). Urine samples collected in the morning and during the day were used to account for deviations in the urine composition, and the universality of the proposed protocol was ensured by performing sample dilution as a pretreatment. The use of calibration plots in the form of Freundlich adsorption isotherms yielded linear calibration plots. All limits of detection were lower than the minimal concentrations required for TDM, equaling 7.5 (CTR), 8.8 (CZL), and 36 (CPR) mu g mL(-1). Comparison of CuNPs with Ag and Au nanoparticles (AgNPs and AuNPs, respectively) confirmed that CuNPs offered a competitively high Raman enhancement efficiency (for excitation at 638 nm). Further, although the CuNPs demonstrated poorer temporal stability as compared with the AgNPs and AuNPs, the use of freshly prepared CuNPs resulted in satisfactory accuracy (recovery = 93-107%). Given the short analysis time (<20 min, including the time for the synthesis of the CuNPs and the SERS measurements using a portable Raman spectrometer), low sensitivity to the presence of the primary intrinsic urine components and satisfactory figures of merit of the proposed protocol for the determination of cephalosporin antibiotics in urine, it should be suitable for use in TDM. (C) 2020 Elsevier B.V. All rights reserved.

Creatinine (CRN) is the component of human biofluids (urine, blood) which is a clinically important indicator for evaluation of various diseases, e.g., renal (dis)functions. This work is dedicated to application of molecularly imprinted silica gel (MISG) as a CRN-selective sorbent for solid phase extraction to improve SERS based detection of CRN in urine. MISG was prepared using sol-gel process in the presence of a template (CRN) and aluminum ions which served as a doping agent to create recognition sites. Spectrophotometry studies showed that the combination of doping and imprinting improves sorption capacity 3 times. We found that doping plays a key role and imprinting without doping does not lead to sorption improvement at all. Hydroxylamine stabilized silver nanoparticles were used as SERS substrate and the maximal CRN signal (i.e., analysis sensitivity) was found in alkaline media. Also, addition of alkali leads to dissolution of MISG matrix that was used to release CRN molecules and speed-up of analysis by skipping elution step. SERS results also demonstrate that MISG possesses the maximal sorption in comparison with silica gels fabricated without imprinting and/or doping. Therefore, the final analysis protocol implies solid phase extraction of CRN from a solution with further pH adjusting of the MISG-CRN complex and SERS detection of the released CRN. The protocol testing using model CRN solution and a urine sample demonstrated possibility for CRN detection at physiologically relevant concentrations and significant reduction of SERS background after extraction step.

This report is dedicated to development of surface-enhanced Raman spectroscopy (SERS) based analysis protocol for detection of antibiotics in urine. The key step of the protocol is the pretreatment of urine before the detection to minimize background signal. The pretreatment includes extraction of intrinsic urine components using aluminum hydroxide gel (AHG) and further pH adjusting of the purified sample. The protocol was tested by detection of a single antibiotic in artificially spiked samples of real urine. Five antibiotics of cephalosporin class (cefazolin, cefoperazone, cefotaxime, ceftriaxone, and cefuroxime) were used for testing. SERS measurements were performed using a portable Raman spectrometer with 638 nm excitation wavelength and silver nanoparticles as SERS substrate. The calibration curves of four antibiotics (cefuroxime is the exception) cover the concentrations required for detection in patient's urine during therapy (25/100‒500 μg/mL). Random error of the analysis (RSD < 20%) and limits of quantification (20‒90 μg/mL) for these antibiotics demonstrate the applicability of the protocol for reliable quantitative detection during therapeutic drug monitoring. The detection of cefuroxime using the protocol is not sensitive enough, allowing only for qualitative detection. Additionally, time stability and batch-to-batch reproducibility of AHG were studied and negative influence of the pretreatment protocol and its limitations were estimated and discussed.

The authors describe a series of simple experiments related to the synthesis, oxidation, and aggregation of plasmonic copper nanoparticles (CuNPs) stabilized by iodide ions. These experiments can help with (i) substituting noble-metal-based plasmonic nanoparticles for nanotechnology-oriented lessons, (ii) demonstrating high reactivity of nanosized objects, and (iii) attracting students' attention by colorful experiments. The main compounds required for the experiments are CuSO4, KI, NaBH4, and diluted H2SO4. These compounds are relatively safe, available, cost-effective, and do not require special recycling. The color of the reaction mixture rapidly changes from colorless (diluted CuSO4) to wine red (fresh CuNPs) and then to yellow (oxidized CuNPs) or dark green and blue (agglomerated CuNPs), making the reactions more visible to the students. The fast oxidation of CuNPs by the oxygen in air was proposed to demonstrate the high reactivity of nanosized copper and to enrich the nanotechnology lessons with chemical reactions. The authors also highlight and discuss the importance of accounting for potential side reactions (e.g., hydrolysis) for the synthesis and oxidation of CuNPs. The important role of iodide ions in providing colloidal stability of CuNPs is discussed, and several comparative experiments with other stabilizers are proposed. In addition, the authors compare the optical properties of CuNPs with those of gold-and silver-based nanoparticles. The experiments are designed to be completed in less than 45 min and have been regularly used at chemistry club lessons for secondary school students in 2017 and 2018. The effitiency of the experiments has also been tested several times with undergraduate students at Saratov State University.

The aim of the work is the microwave-assisted (MW) synthesis of SERS-active copper nanoparticles (CuNPs) and the core-shell composite based on nanostructured copper layer deposited over CaCO3 microspheres (CaCO3@Cu; 1.4±0.4 μm). The comparison of MW synthesized CuNPs and gold nanoparticles showed the equal orders of magnitude of the Raman enhancement. The temporal stability of CaCO3@Cu samples was found significantly better than that of CuNPs: 4 days vs. 30 min. Stabilizer- and organic solvent-free synthesis of CaCO3@Cu enables to minimize background SERS signal. The applicability of CaCO3@Cu for chemical analysis was showed by detection of antibiotic drug (ceftriaxone) in a range of concentrations which is relevant for practical purposes (5–500 μg/mL).

The work is dedicated to fabrication and study of SERS-active nanocomposites based on aluminum hydroxide with incorporated copper nanoparticles (CuNP; 10 +/- 2 nm). The initial CuNP and the final composite were characterized using SEM, EDX, STM, and absorbance spectroscopy in UV-visible range. The application of incorporation enabled to improve temporal stability of SERS-activity of the CuNP against oxidation to around 80 times compare to colloidal CuNP; the composite is SERS-active for more than 8 days. The value of Raman enhancement was found around 8x10(6) that is comparable with the values for silver and gold based SERS substrates. The applicability of the final composite for chemical analysis was demonstrated by SERS detection of some drugs, such as antitumor (methotrexate) and antibacterial drugs (lincomycin, sulfadimethoxine, ceftriaxone). The analytes were detected at concentrations which have to be detected at physiological conditions in urine (50-100 mu g/mL) after medical treatment.