Electrochemical biosensor for sensitively simultaneous determination of dopamine, uric acid, guanine, and adenine based on poly-melamine and nano Ag hybridized film-modified electrode

Redox probe-free electrochemical immunosensor utilizing electropolymerized melamine on reduced graphene oxide for the point-of-care diagnosis of gastric cancer

Pepsinogen I (PG I) is a biomarker that plays a crucial role in the diagnosis of gastric cancer. The development of biosensor to monitor PG I overexpression in serum is crucial for early gastric cancer diagnosis, offering a less invasive alternative to the costly and uncomfortable gastroscopy procedure. This study presents a cost-efficient, scalable and disposable label-free biosensing strategy for detecting PG I, utilizing a redox-active polymelamine electrodeposited on a reduced graphene oxide screen-printed electrode surface (PM-rGO/SPE). Under optimized conditions, the conducting polymer PM was deposited on the rGO/SPE via a potentiodynamic method. The structural and morphological features of PM-rGO/SPE were analyzed with the assistance of Raman and Scanning Electron Microscopy analysis. Specific monoclonal anti-PG I antibodies were immobilized on the in situ prepared redox-active layer via EDC/NHS chemistry to develop a novel electrochemical immunosensor. Unlike the traditional immunosensing strategies which utilizes external redox probe solution for measuring the signal, the developed configuration allowed for redox-probe free monitoring of current changes of the redox active PM resulting from the formation of the immunocomplex on the electrode surface. Utilizing this method, PG I detection spanned a clinically relevant concentration range of 0.01-200 ng/mL, with a low limit of detection at 9.1 pg/mL. The electrochemical immunosensor demonstrated specificity against other biomarkers such as PDCD1, ErBb2, and CD28 with negligible interference. The immunosensor exhibited excellent recovery capabilities for PG I detection in serum samples. These findings underscore the potential of the PM-rGO/SPE immunosensor as a point-of-care diagnostic tool for gastric cancer.

Plasmonic-magnetic nanorobots for SARS-CoV-2 RNA detection through electronic readout

The coronavirus disease 2019 (COVID-19) has prompted an urgent demand for nanotechnological solutions towards the global healthcare crisis, particularly in the field of diagnostics, vaccines, and therapeutics. As an emerging tool for nanoscience and technology, micro/nanorobots have demonstrated advanced performances, such as self-propelling, precise maneuverability, and remote actuation, thus hold great potential to provide breakthroughs in the COVID-19 pandemic. Here we show a plasmonic-magnetic nanorobot-based simple and efficient COVID-19 detection assay through an electronic readout signal. The nanorobots consist of Fe₃O₄ backbone and the outer surface of Ag, that rationally designed to perform magnetic-powered propulsion and navigation, concomitantly the probe nucleic acids transport and release upon the hybridization which can be quantified with the differential pulse voltammetry (DPV) technique. The magnetically actuated nanorobots swarming enables enhanced micromixing and active targeting, thereby promoting binding kinetics. Experimental results verified the enhanced sensing efficiency, with nanomolar detection limit and high selectivity. Further testing with extracted SARS-CoV-2 viral RNA samples validated the clinical applicability of the proposed assay. This strategy is versatile to extend targeting various nucleic acids, thus it could be a promising detection tool for other emerging pathogens, environmental toxins, and forensic analytes.

A review of applications of surface-enhanced raman spectroscopy laser for detection of biomaterials and a quick glance into its advances for COVID-19 investigations

Surface-enhanced Raman spectroscopy (SERS) is one of the most sensitive analytical tools. In some cases, it is possible to record a high-quality SERS spectrum in which even a single molecule is involved. Therefore, SERS is considered a significantly promising option as an alternative to routine analytical techniques used in food, environmental, biochemical, and medical analyzes. In this review, the definitive applications of SERS developed to identify biochemically important species (especially medical and biological) from the simplest to the most complex are briefly discussed. Moreover, the potential capability of SERS for being used as an alternative to routine methods in diagnostic and clinical cases is demonstrated. In addition, this article describes how SERS-based sensors work, addresses its advancements in the last 20 years, discusses its applications for detecting Coronavirus Disease 2019 (COVID-19), and finally describes future works. The authors hope that this article will be useful for researchers who want to enter this amazing field of research.

Simultaneous determination of guanine and adenine in human saliva with graphite sparked screen-printed electrodes

Saliva represents one of the most useful biological samples for non-invasive testing of health status and diseases prognosis and therefore, the development of advanced sensors enabling the determination of biomarkers in unspiked human whole saliva is of immense importance. Herein, we report on the development of a screen-printed graphite sensor modified with carbon nanomaterials generated by spark discharge for the determination of guanine and adenine in unspiked human whole saliva. The designed sensor was developed with a "green", extremely simple, fast (16 s), fully automated "linear mode" sparking process implemented with a 2D positioning device. Carbon nanomaterial-modified surfaces exhibit outstanding electrocatalytic properties enabling the determination of guanine and adenine over the concentration range 5 - 1000 nM and 25 - 1000 nM, while achieving limits of detection (S/N 3) as low as 2 nM and 8 nM, respectively. The sensor was successfully applied to the determination of purine bases in unspiked human whole saliva following a simple assay protocol based on ultrafiltration that effectively alleviates biofouling issues. Recovery was 96-108%.

Nanosized iron telluride for simultaneous nanomolar voltammetric determination of dopamine, uric acid, guanine and adenine

Herein, an efficient electrochemical sensor based on nano-sized iron telluride material (FeTe₂) have been developed for the first time for simultaneous nanomolar determination of dopamine, uric acid, guanine and adenine molecules.

Poly(glycine)/graphene oxide modified glassy carbon electrode: Preparation, characterization and simultaneous electrochemical determination of dopamine, uric acid, guanine and adenine

A novel poly(glycine) (p-GLY)/graphene oxide (GO) composite based sensor (p-GLY/GO) was successfully prepared on glassy carbon electrode by simple electropolymerization. Electrochemical responses of analytes on p-GLY/GO modified electrode were studied by cyclic voltammetry and differential pulse voltammetry. The results demonstrated that p-GLY/GO modified electrode showed a favorable application for the simultaneous determination of dopamine (DA), uric acid (UA), guanine (GU) and adenine (AD). Owing to the synergistic effect of p-GLY and GO, the oxidation peaks of four analytes separated well from each other, and the potential separations of oxidation peaks of DA-UA, UA-GU and GU-AD were large up to 170, 350 and 300 mV, respectively. As-prepared p-GLY/GO modified electrode offered wide linear responses for DA, UA, GU and AD over the ranges of 0.20-62, 0.10-105, 0.15-48 and 0.090-103 μM with detection limits of 0.011, 0.061, 0.026 and 0.030 μM (S/N = 3), respectively. Moreover, p-GLY/GO modified electrode presented favorable selectivity, stability and reproducibility, which was a promising candidate as an electrochemical sensor for the simultaneous determination of DA, UA, GU and AD.

Raman Computational and Experimental Studies of Dopamine Detection

A combined theoretical and experimental analysis of dopamine (DA) is presented in this work with the objective of achieving more accurate detection and monitoring of this neurotransmitter at very low concentrations, specific to physiological levels. Surface-enhanced Raman spectroscopy on silver nanoparticles was employed for recording DA concentrations as low as 10-11 molar. Quantum chemical density functional calculations were carried out using Gaussian-09 analytical suite software. Relatively good agreement between the simulated and experimentally determined results indicates the presence of different DA molecular forms, such as uncharged DA±, anionic DA-, and dopaminequinone. Disappearance of the strongest bands of dopamine around 750 cm-1 and 790 cm-1, which suggests its adsorption onto the metallic surface, is not only consistent with all of these DA configurations, but also provides additional information about the analyte's redox process and voltammetric detection. On the other hand, occurrence of the abovementioned Raman lines could indicate the formation of multilayers of DA or its presence in a cationic DA⁺ form. Thus, through coordinated experiment and theory, valuable insights into changes observed in the vibrational signatures of this important neurotransmitter can be achieved for a better understanding of its detection at physiological levels, which is crucial if further optovoltammetric medical device development is envisioned.

Simultaneous determination of guanine and adenine in the presence of uric acid by a poly(para toluene sulfonic acid) mediated electrochemical sensor in alkaline medium

Simultaneous sensing of guanine and adenine in presence of uric acid in alkaline medium by polymer modified electrode.

Simultaneous Determination of Dopamine, Uric Acid and Guanine at Polyadenine Film Modified Electrode

A polyadenine film (PAE) modified glassy carbon electrode (GCE) was employed for the simultaneous determination of dopamine (DA), uric acid (UA) and guanine (GA). Experimental results showed that this modified electrode had good electrocatalytic properties for the oxidation of DA, UA and GA. Under optimal conditions, DA, UA and GA reflected their electrochemical response into three separated and well-defined oxidation peaks, whose currents increased 47-, 12-, and 7-fold, respectively, compared with those at bare electrode. Moreover, their oxidation peak currents were linear proportional to their concentrations within the ranges of 2.5 - 75, 10 - 750, and 7.5 - 75 μmol L(-1), respectively, and the limits of detection (LOD) (S/N = 3) were 0.075, 0.35, and 0.025 μmol L(-1), respectively. Compared with a variety of modified electrodes, this designed sensor had a wider linear range and lower LOD. Furthermore, the sensor exhibited good stability and reproducibility.

Functionalized solid electrodes for electrochemical biosensing of purine nucleobases and their analogues: a review

Interest in electrochemical analysis of purine nucleobases and few other important purine derivatives has been growing rapidly. Over the period of the past decade, the design of electrochemical biosensors has been focused on achieving high sensitivity and efficiency. The range of existing electrochemical methods with carbon electrode displays the highest rate in the development of biosensors. Moreover, modification of electrode surfaces based on nanomaterials is frequently used due to their extraordinary conductivity and surface to volume ratio. Different strategies for modifying electrode surfaces facilitate electron transport between the electrode surface and biomolecules, including DNA, oligonucleotides and their components. This review aims to summarize recent developments in the electrochemical analysis of purine derivatives, as well as discuss different applications.

Simultaneous determination of hydroxylamine and phenol using a nanostructure-based electrochemical sensor

The electrochemical oxidation of hydroxylamine on the surface of a carbon paste electrode modified with carbon nanotubes and 2,7-bis(ferrocenyl ethyl)fluoren-9-one is studied. The electrochemical response characteristics of the modified electrode toward hydroxylamine and phenol were investigated. The results showed an efficient catalytic activity of the electrode for the electro-oxidation of hydroxylamine, which leads to lowering its overpotential. The modified electrode exhibits an efficient electron-mediating behavior together with well-separated oxidation peaks for hydroxylamine and phenol. Also, the modified electrode was used for determination of hydroxylamine and phenol in some real samples.