Application of spectroelectroanalysis for the quantitative determination of mixtures of compounds with highly overlapping signals

Electrochemical immunosensor AuNPs/NG-PANI/ITO-PET for the determination of BDNF in depressed mice serum

A novel electrochemical immunosensor was developed for highly sensitive detection of brain-derived neurotrophic factor (BDNF), a well-known depression marker. The immunosensor was fabricated by modifying indium tin oxide-coated polyethylene terephthalate (ITO-PET) with N-doped graphene-polyaniline (NG-PANI) and gold nanoparticles (AuNPs) to enhance the conductivity and protein loading capacity. Subsequently, BDNF was immobilized onto the electrode surface via gold-sulfur bonds, followed by the attachment of biotinylated antibody (Biotin-Ab) and horseradish peroxidase-avidin (HRP-Avidin) to create the final immunosensor (HRP-Avidin-Biotin-Ab-BDNF-AuNPs/NG-PANI/ITO-PET). The proposed immunosensor exhibited a linear range of determination (0.781-400 pg/mL) with a low limit of detection (LOD) of 0.261 pg/mL (S/N = 3) and excellent reproducibility (RSD = 1.4%) and stability (92.7%, RSD = 3.1%). Additionally, the immunosensor demonstrated good anti-interference performance and good recovery (98.1-107%). To evaluate the practical utility of the immunosensor, BDNF levels were quantified in the serum of mice with depression induced by chronic unpredictable mild stress (CUMS). The results indicated that the serum BDNF levels were significantly decreased in the depression model group compared with the control group, highlighting the potential of this immunosensor for clinical detection of BDNF in depression diagnosis and treatment.

Recent State and Challenges in Spectroelectrochemistry with Its Applications in Microfluidics

This review paper presents the recent developments in spectroelectrochemical (SEC) technologies. The coupling of spectroscopy and electrochemistry enables SEC to do a detailed and comprehensive study of the electron transfer kinetics and vibrational spectroscopic fingerprint of analytes during electrochemical reactions. Though SEC is a promising technique, the usage of SEC techniques is still limited. Therefore, enough publicity for SEC is required, considering the promising potential in the analysis fields. Unlike previously published review papers primarily focused on the relatively frequently used SEC techniques (ultraviolet-visible SEC and surface-enhanced Raman spectroscopy SEC), the two not-frequently used but promising techniques (nuclear magnetic resonance SEC and dark-field microscopy SEC) have also been studied in detail. This review paper not only focuses on the applications of each SEC method but also details their primary working mechanism. In short, this paper summarizes each SEC technique's working principles, current applications, challenges encountered, and future development directions. In addition, each SEC technique's applicative research directions are detailed and compared in this review work. Furthermore, integrating SEC techniques into microfluidics is becoming a trend in minimized analysis devices. Therefore, the usage of SEC techniques in microfluidics is discussed.

Spectroelectrochemistry as a new tool for the quantification of UV filters in sun creams

This study focuses on the spectroelectrochemical quantification of four UV filters, butylmethoxy dibenzoylmethane (BM), benzophenone-3 (BP3), ethylhexyl methoxycinnamate (EM) and octocrylene (OC) used as sunscreens in cosmetics. Three of them exhibited electrochemical activity resulting in the modification of their absorption spectrum under the application of an oxidizing potential of +1.8 V vs. Ag. When working with a mixture containing both electroactive and nonelectroactive UV filters, UV-vis absorption spectra recorded before and after the application of the potential differed. The combination of spectral deconvolution of the spectra pair allowed a more accurate identification and quantification of UV filters than spectral deconvolution of the initial absorbance spectrum alone. This method was effective for the assessment of UV filters in model mixtures and commercial sun creams.

UV/Vis absorption spectroelectrochemistry of folic acid

UV/Vis absorption spectroelectrochemistry is a very promising analytical technique due to the complementary information that is simultaneously obtained from electrochemistry and spectroscopy. In this work, this technique is used in a parallel configuration to study the oxidation of folic acid in alkaline medium. Herein, UV/Vis absorption spectroelectrochemistry has been used to detect both the oxidation products and the folic acid consumed at the electrode/solution interface, allowing us to develop an analytical protocol to quantify vitamin B9 in pharmaceutical tablets. Linear ranges of three orders of magnitude have been achieved in basic medium (pH = 12.9), obtaining high repeatability and low detection limits. The spectroelectrochemical determination of folic acid in pharmaceutical tablets at alkaline pH values is particularly interesting because of the changes that occur in the optical signal during the electrochemical oxidation of FA, providing results with very good figures of merit and demonstrating the utility and versatility of this hyphenated technique, UV/Vis absorption spectroelectrochemistry.

Spectroelectrochemical Determination of Isoprenaline in a Pharmaceutical Sample

UV/Vis absorption spectroelectrochemistry (SEC) is a multi-response technique that has been commonly used for the characterization of materials and the study of reaction mechanisms. However, it has been scarcely used for quantitative purposes. SEC allows us to obtain two analytical signals simultaneously, yielding a dual sensor in just one experiment. In the last years, our group has developed new devices useful for analysis. In this work, a SEC device in parallel configuration, based on optical fibers fixed on screen-printed electrodes, was used to determine isoprenaline in a commercial drug, using both, the electrochemical and the spectroscopic signals. In this commercial drug, isoprenaline is accompanied in solution by other compounds. Among them is sodium metabisulfite, an antioxidant that strongly interferes in the isoprenaline determination. A simple pretreatment of the drug sample by bubbling wet-air allows us to avoid the interference of metabisulfite. Here, we demonstrate again the capabilities of UV/Vis absorption SEC as double sensor for analysis and we propose a simple pretreatment to remove interfering compounds.

Determination of uric acid in synthetic urine by using electrochemical surface oxidation enhanced Raman scattering

In this work, a new and easy methodology to determine uric acid in relevant samples using Raman spectroelectrochemistry is presented. The spectroelectrochemistry experiment is based on the in-situ formation of a suitable substrate that enables the enhancement of the Raman signal of an analyte during the oxidation stage of a silver electrode. This phenomenon is known as electrochemical surface oxidation enhanced Raman scattering (EC-SOERS) and has proved to be useful in quantitative analysis using disposable screen printed electrodes. The successful combination of EC-SOERS with PARAFAC analysis allows the determination of uric acid in a relevant complex sample avoiding the use of standard addition method and without using a baseline correction, which simplifies the application of such methodology in routine analysis.

A Flexible Platform of Electrochemically Functionalized Carbon Nanotubes for NADH Sensors

A flexible electrode system entirely constituted by single-walled carbon nanotubes (SWCNTs) has been proposed as the sensor platform for β-nicotinamide adenine dinucleotide (NADH) detection. The performance of the device, in terms of potential at which the electrochemical process takes place, significantly improves by electrochemical functionalization of the carbon-based material with a molecule possessing an o-hydroquinone residue, namely caffeic acid. Both the processes of SWCNT functionalization and NADH detection have been studied by combining electrochemical and spectroelectrochemical experiments, in order to achieve direct evidence of the electrode modification by the organic residues and to study the electrocatalytic activity of the resulting material in respect to functional groups present at the electrode/solution interface. Electrochemical measurements performed at the fixed potential of +0.30 V let us envision the possible use of the device as an amperometric sensor for NADH detection. Spectroelectrochemistry also demonstrates the effectiveness of the device in acting as a voltabsorptometric sensor for the detection of this same analyte by exploiting this different transduction mechanism, potentially less prone to the possible presence of interfering species.