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.Ministerio de Economía y Competitividad (Grants CTQ2017-83935-R-AEI/FEDERUE) and Junta de Castilla y León (Grant BU297P18

Effect of chloride and pH on the electrochemical surface oxidation enhanced Raman scattering

In the present work, electrochemical surface oxidation enhanced Raman scattering (EC-SOERS) was studied using time resolved Raman spectroelectrochemistry. This multiresponse technique allows us to obtain dynamic information about the processes taking place during the electrochemical oxidation of a silver substrate. EC-SOERS is particularly found in specific electrolytic conditions, namely, HClO4 0.1 M + KCl 5·10−3 M, and has a clear dependence on chloride concentration and pH, being the optimum values between 5·10−3 M and 1·10−2 M for chloride and pH = 1. In light of the results of this study, the appearance of the phenomenon is related to the modification of the electrode surface, yielding Ag/AgCl cubes as plasmonic structures, and the stability of such structures at low pH values. The results presented in this work could shed more light into the intricate EC-SOERS phenomenon which can be summarized as the increase of the Raman signal for a Raman probe molecule exclusively during the electrochemical oxidation of silver electrodes.Ministerio de Economía y Competitividad (Grants CTQ2017-83935-R-AEI/FEDERUE) and Junta de Castilla y León (Grant BU033-U16). J.V.P-R. thanks JCyL for his postdoctoral fellowship (Grant BU033-U16

Electrochemical SERS and SOERS in a single experiment: A new methodology for quantitative analysis

In the present work, a new methodology which combines two different phenomena to enhance the Raman signal is used to resolve a mixture of two compounds with similar molecular structures. The use of Raman spectroelectrochemistry (Raman-SEC) allows us to collect simultaneously, with high time-resolution, the enhancement of the Raman signal of the compounds present in a sample during the electrochemical oxidation-reduction cycle (ORC) of a silver screen-printed electrode. During such ORC two different phenomena appears depending on the stage of the electrochemical modification of the silver substrate, which are known as electrochemical surface enhanced Raman scattering (EC-SERS) and electrochemical surface oxidation enhanced Raman scattering (EC-SOERS). This work is a proof of concept that demonstrates the advantage of using EC-SOERS and EC-SERS in a single experiment to resolve mixtures of similar molecules such as vitamin B3, which components are nicotinic acid and nicotinamide. Although the interaction between analytes and substrates influence a univariate calibration, the trilinear character of Raman-SEC makes possible to deconvolve such interactions and provide a good calibration curve for both, nicotinic acid and nicotinamide.Ministerio de Economía y Competitividad (Grants CTQ2017-83935-R-AEI/FEDERUE), Junta de Castilla y León (Grant BU033-U16 and BU297P18) and Ministerio de Ciencia, Innovación y Universidades (RED2018-102412-T). J.V.P-R. thanks JCyL for his postdoctoral fellowship (Grant BU033-U16

Spectroelectrochemistry of Quantum Dots

Spectroelectrochemistry (SEC) is a set of techniques with many advantages in the study and characterization of materials. Although SEC has not yet been widely used to study quantum dots (QDs), the information extracted from SEC experiments about these nanostructures is very useful. Most of the works that use SEC to study QDs are high-quality pieces of research. This review intends to show how to perform SEC in an easy way and what information can be obtained using these techniques. Most of the examples shown in this review are related to semiconductor and carbon QDs. After a brief introduction, some optoelectronic properties of QDs and the main SEC techniques are described. The capabilities of SEC for the study of QDs are illustrated with examples extracted from literature. Finally, the needs of SEC to become a user-friendly technique and its evolution to become more powerful are commented in the last section of the review.Ministerio de Economía y Competitividad (Grants CTQ2017-83935-R-AEI/FEDERUE) and Junta de Castilla y León (Grant BU033-U16 and BU297P18). J.G-R. thanks UBU for his postdoctoral contract. J.V.P-R. thanks JCyL for his postdoctoral fellowship (Grant BU033-U16). Thanks to J

Enhancement factors in electrochemical surface oxidation enhanced Raman scattering

Electrochemical Surface Oxidation Enhanced Raman Scattering (EC-SOERS) is a new phenomenon that provokes the enhancement of the Raman signal during the oxidation of a metal surface. Studies carried out so far indicate that carbonyl and carboxyl group are necessary to observe this phenomenon with a delocated charge being an important factor. In this work, the enhancement factors of EC-SOERS for different molecules, which present highly delocated charge and a carboxyl group, have been assessed. The systematic study of the enhancement factors helps to shed more light on the interaction of the molecules with the electrochemically generated SOERS substrates, yielding key information about the properties and specific features of this intriguing phenomenon. For the first time, a systematic information about the enhancement factors of this phenomenon is obtained. Analytical enhancement factors higher than 105 are obtained.Ministerio de Economía, y Competitividad (Grant CTQ2017-83935-R-AEI/FEDERUE), Junta de Castilla y León (Grant BU297P18) and Ministerio de Ciencia, Innovación y Universidades (Grant RED2018-102412-T). J.V.P-R. thanks Junta de Castilla y León for his postdoctoral fellowship (Grant BU033-U16)

Chemical selectivity in electrochemical surface oxidation enhanced Raman scattering

Electrochemical Surface Oxidation Enhanced Raman Scattering (EC-SOERS) is an interesting and promising phenomenon capable of amplifying the Raman signal in a similar way to Surface Enhanced Raman Scattering (SERS), but EC-SOERS takes place during the oxidation of a silver substrate. This phenomenon was originally described for specific electrolytic conditions in which a small amount of chloride in acidic medium was mandatory to obtain a substantial enhancement. Herein, we demonstrate that EC-SOERS can be also observed in presence of KBr, showing a potential-dependent behavior. Moreover, in this work a novel approach to reach chemical selectivity during time resolved Raman spectroelectrochemistry (TR-Raman-SEC) experiments is proposed. This new approach is based on the effect of the electrolytic medium on the structures that are formed on the electrode surface. SEM studies were carried out to study the origin of this selectivity. Although SEM images reveal clear differences between the structures of silver halides formed on the electrode surface during the oxidation of the substrate, the absence of EC-SOERS effect at open circuit potential hinders the identification of the actual structures responsible for the phenomenon.Ministerio de Economía y Competitividad (Grants CTQ2017-83935-R-AEI/FEDERUE), Junta de Castilla y León (BU297P18) and Ministerio de Ciencia, Innovación y Universidades (RED2018-102412-T

Quantitative Raman spectroelectrochemistry using silver screen-printed electrodes

Surface enhanced Raman scattering (SERS) is a powerful technique based on the intensification of the Raman signal because of the interaction of a molecule with a nanostructured metal surface. Electrochemically roughened silver has been widely used as SERS substrate in the qualitative detection of analytes at the ultra-trace level. However, its potential for quantitative analysis has not been widely exploited yet. In this work, the combination of time-resolved Raman spectroelectrochemistry with silver screen-printed electrodes (SPE) is proposed as a novel methodology for the preparation of SERS substrates. The in situ activation of a SERS substrate is performed simultaneously with the analytical detection of a probe molecule, controlling the process related to the preparation of the substrate and performing the analytical measurement in real time. The results show the good performance of silver SPE as electrochemically-induced surface-enhanced Raman scattering substrates. Raman spectra were recorded at fairly low integration times (250 ms), obtaining useful spectroelectrochemical information of the processes occurring at the SPE surface with excellent time-resolution. By recording the microscopic surface images at different times during the experiment, we correlated the different data obtained: structural, optical and electrochemical. Finally, the in situ activation process was used to obtain a suitable in situ SERS signal for ferricyanide and tris(bipyridine)ruthenium (II) quantification. The detection of the analytes at concentrations of a few tens of nM was possible with a low integration time (2 s) and good precision, demonstrating the exceptional performance of the Raman spectroelectrochemical method and the possibility to use cost-effective screen-printed electrodes for applications where a high sensitivity is needed.Ministerio de Economía y Competitividad (CTQ2017-83935-R, CTQ2014-55583-R, TEC2014-51940-C2-2R, CTQ2015-71955-REDT) and Junta de Castilla y León (BU033-U16

Dataset of the work “Simultaneous Raman and reflection UV/Vis absorption spectroelectrochemistry”

In the present work, a new combination of Raman and ultraviolet and visible (UV/Vis) absorption spectroelectrochemistry in reflection mode is proposed. The new experimental setup allows obtaining the two kinds of spectroscopic data without interferences concomitantly with the electrochemical information. To the best of our knowledge, it is the first time to report the simultaneous obtention of electrochemical, electronic, and vibrational information in the same experiment. This new combination provides time-resolved information about the processes that are taking place on the electrode/solution interface which has significant implications in different fields of chemistry, such as modification of electrodes, studies of electrocatalytic reaction mechanisms, development of sensors, among others. Two different systems were used to demonstrate the advantages and capabilities of the brand-new technique, namely, the oxidation of potassium ferrocyanide, an out-sphere system that is usually employed in the validation of SEC techniques, and the electrochemical-surface enhanced Raman spectroscopy (EC-SERS) detection of crystal violet by in-situ formation of the silver SERS substrate, where the UV/Vis spectra were used to follow the formation of the SERS substrate, whereas the Raman response of a probe molecule was used to confirm either the formation of a nanostructured surface and to obtain the fingerprint of the molecule with a high time resolution. The brand-new experimental setup has shown to be useful, versatile, robust, compact, and easy to use for future applications.Authors acknowledge the financial support from Ministerio de Ciencia e Innovacion (No. PID2020-113154RB-C21), Ministerio de Economía, Industria y Competitividad (No. CTQ2017-83935-RAEI/FEDERUE), Junta de Castilla y Leon (No. BU297P18), and Ministerio de Ciencia, Innovacion y Universidades (No. RED2018-102412-T). J.V.P-R acknowledges Spanish Ministry of Economy, Industry, and Competitiveness for the Juan de la Cierva postdoctoral (No. FJCI-2017-32458) and the University of Alcala (No. CCG19/CC-071). S.H. thanks JCyL and European Social Fund for her predoctoral fellowship

Electrochemical surface oxidation enhanced Raman scattering

In this work, an unexpected enhancement of the Raman signal for uric acid during the electrochemical oxidation of a silver electrode is presented. This behavior cannot be easily explained using classical models of Surface Enhanced Raman Scattering (SERS). Time resolved Raman spectroelectrochemistry is used to study this interesting process strongly dependent on the experimental conditions. The new phenomenon was observed in different molecules and was found to be reproducible and robust, allowing us to use this methodology for the determination of citric acid. The enhancement of the Raman signal only takes place when a potential is applied to the electrode and therefore, this new phenomenon can be denoted as Electrochemical Surface Oxidation Enhanced Raman Scattering (EC-SOERS). In this work, EC-SOERS is presented not only as an alternative to SERS for detection of molecules but also as a reproducible process that can be used for quantitative analysisMinisterio de Economía y Competitividad (Grants CTQ2017-83935-R-AEI/FEDER-UE and CTQ2014-55583-R) and Junta de Castilla y León (Grant BU033-U16

Photoactive Au@MoS2 Micromotors for Dynamic Surface-Enhanced Raman Spectroscopy Sensing

Photophoretic Au@MoS2 micromotors are used as smart mobile substrates for dynamic surface-enhanced Raman spectroscopy (SERS) sensing. The photophoretic capabilities and swarming-like propulsion of the micromotors allow for their schooling and accumulation in the measuring spot, increasing the density of SERS-active gold nanoparticles for Raman mapping and, simultaneously, the preconcentration of the target analyte. The generation of "hot-microflake spots" directly in the Raman irradiation point results in a 15-18-fold enhancement in the detection of crystal violet without the requirement for additional external sources for propulsion. Moreover, the reproducible collective micromotor motion does not depend on the exact position of the laser spot concerning individual micromotors, which greatly simplifies the experimental setup, avoiding the requirements of sophisticated equipment. The strategy was further applied for the detection of malachite green and paraquat with a good signal enhancement. The new on-the-move-based SERS strategy holds great promise for on-site detection with portable instrumentation in a myriad of environmental monitoring and clinical applications.Ministerio de Ciencia e InnovaciónEuropean Commissio