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The sensing modified electrode was prepared using glucose oxidase immobilized onto vanadium pentoxide xerogel with glass/FTO as support electrode to evaluate the possibility to construct a V 2 O 5 /GOx Extended Gate Field Effect Transistor biosensor. Previously, our studies exhibited a sensitivity of V 2 O 5 of 58.1 mV/pH. The use of Nafion® onto V 2 O 5 /GOx caused a decrease of mass loss after several cycles compared to the modified electrode without Nafion® during the EQCM and cyclic voltammetrics studies. Electrical characterization of V 2 O 5 /GOx demonstrated a tendency to stability after 200 s as a function of applied current. In presence of glucose and in different pH, the current decreased when the glucose concentration increased due to the lower active sites of enzyme. After ten voltammetric cycles, the total charge tends to structural stability. In pH = 5.0, the modified electrode based on V 2 O 5 /GOx Extended Gate Field Effect Transistor presented more tendency to sensitivity in different concentration of glucose., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Non-structural 1 (NS1) is a protein biomarker that can be found in blood in the early stages of dengue and related infections (Zika and Chikungunya). This study aims to develop a biosensor to selectively quantify NS1 using DNA aptamer co-immobilized on gold electrodes with 6-(ferrocenyl)hexanethiol (FCH) using electrochemical capacitive spectroscopy. This technique uses a redox probe (FCH) immobilized on the self-assembled monolayer to convert impedance into capacitance information. The developed platform was blocked with bovine serum albumin before NS1 exposure and the ratio between aptamers and FCH was optimized. The aptasensor was tested using commercial NS1 serotype 4 in phosphate-buffered saline and commercial undiluted human serum. Using the optimum applied potential provides high sensitivity (3 and 4 nF per decade) and low limit of detection (30.9 and 41.8 fg/mL) with a large linear range (10 pg to 1 µg/mL and 10 pg to 100 ng/mL, respectively). Both results exhibit a residual standard deviation value < 1%. The results suggested that this aptasensor was capable of detecting NS1 in the clinical range and can be applied to any other specific aptamer with FCH, opening the path for label-free miniaturized point-of-care devices with high sensitivity and specificity., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Dengue is one of the most commonly neglected tropical diseases transmitted by Aedes aegypti infected with Dengue virus. This virus belongs to the gender Flavivirus and produces a non-structural protein 1 (NS1), which is an important biomarker found at high levels in blood in early disease stage. Therefore, this study focused on the development of an electrochemical biosensor for NS1 detection using DNA aptamers. Gold electrodes were co-immobilized with specific aptamers and 6-mercapto-1-hexanol (MCH) to obtain a self-assembled monolayer. The molar ratio between aptamers and MCH was optimized and the platform characterized by electrochemical impedance spectroscopy and atomic force microscopy. Bovine serum albumin was added in NS1 solution to stabilize it and block the surface to avoid non-specific interactions. The biosensor performance was tested with NS1 protein serotype 4 (in phosphate saline buffer and human serum) and with a solution of serotype 1 in human serum. The results showed a sensitivity of 2.9%, 2.7% and 1.7% per decade, respectively, and low limit of detection (0.05, 0.022 and 0.025 ng/mL). The platform was also tested with Envelope protein as negative control. Furthermore, the aptamer sensor was able to detect NS1 in clinical range and it is a promising candidate for a new class for miniaturized point-of-care device for different Dengue serotypes., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Breast cancer remains one of the leading causes of women death. The development of more sensitive diagnostic tests, which could present a faster response, lower cost, and could promote early diagnosis would increase the chances of survival. This study reports the development and optimization of an electrochemical aptasensor for the detection of HER2 protein, a breast cancer biomarker. Two sensing platforms were developed on gold screen-printed electrodes. The first platform is composed of self-assembled monolayer (SAM) made from mixture of thiolated DNA aptamers specific for HER2 and 1-mercapto-6-hexanol (MCH), while the second one is a ternary SAM composed of the same aptamer and 1,6-hexanethiol (HDT). Both platforms were further passivated with MCH and blocked with bovine serum albumin. The biosensors were characterized using electrochemical impedance spectroscopy to detect the target protein from 1 pg/mL to 1 μg/mL in phosphate buffered saline, diluted and undiluted human serum through charge transfer resistance value. The ternary SAM architecture shows a reduction of non-specific attachment to the electrode surface due to the HDT antifouling properties. In addition, this platform exhibits 172 pg/mL as limit of detection and a sensitivity of 4.12% per decade for undiluted serum compared with SAM architecture with the 179 pg/mL and 4.32% per decade, respectively. Electrochemical aptasensors are highly promising for medical diagnostic and ternary layers could improve the limit of detection., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Analytical sensors that can detect chemical (including biological) analytes are becoming increasingly widespread within the field of analytical chemistry. More than this, in a world tending towards the 'internet-of-things', the miniaturization of such devices is becoming increasingly urgent. Accordingly, electrochemical methods that are simultaneously multiplexable and effective at a miniature scale are receiving much attention. In the present work, we compare the label-free electrochemical response of enzymatic biosensors with the response of their optical counterpart. As a proof-of-concept we compare the electrochemical impedimetric response and the first time described capacitive response of enzymatic biosensors to their optical reflectance response (measured in the visible region using a portable handset spectrophotometer). The target was the detection of glucose and urea. The chemical platform of the sensors was composed of enzymatically functionalized polyaniline thin films. Sensitivity, linearity, and the limit of detection were analyzed for both electrochemical and optical instrumental settings. We found that the impedimetric/capacitive electrochemical setup produced a response that was of a similar quality to the optical response (sensitivities of 10.7 ± 0.7, 7.4 ± 0.7 and 4.3 ± 0.2% per decade for impedimetric, capacitive and optical glucose biosensors, respectively) with a broader linear range (10 -4 to 10 -1 mol L -1 for both glucose and urea biosensors) and similar limit-of-detection in the range of 1 μmol L -1 within a relevant and practical diagnosis range for biomedical applications.

Glucose and urea enzymatic biosensors were fabricated. One-step electrochemical immobilization process was used to produce thin polyaniline films with entrapped enzymes. Chronopotentiometric analysis, scanning electron microscopy, electrochemical impedance spectroscopy and optical reflectance spectroscopy were used to determine the structure-property relationship of the functionalized polymeric thin films. The device has a recognition stage connected to a potentiometric field-effect-transistor stage and is based on the measurement of microenvironment pH variation or locally produced ions. Optimization of biosensor fabrication and effective measurement conditions were performed. The optimized films presented sensitivity, linearity and detection range to glucose of 14.6 ± 0.4 mV/decade, 99.8% and from 10 -4  M to 10 -1  mol/L. Two different biosensors were produced based on the enzymatic reaction of urea with selectivity to ammonium or hydroxyl ions. For ammonium ion selective film, the sensor's parameters were 14.7 ± 0.9 mV/decade, 98.2% and from 10 -5 to 10 -1  mol/L. For the hydroxyl ion selective film, the same parameters were 7.4 ± 0.5 mV/decade, 98.1% and from 10 -5 to 10 -1  mol/L. The change in the oxidation state of the polymeric matrix explains: i) the large loss of functionality of glucose biosensor in time, ii) the conservation of functionality to the hydroxyl ions for urea biosensor and iii) the selectivity variation of the ammonium ion selective urea biosensor. The results indicate that the polymeric matrix has indeed changeable selectivity, what can be applied in different situations for biosensors production.

We report the development of a simple and powerful capacitive aptasensor for the detection and estimation of human epidermal growth factor receptor 2 (HER2), a biomarker for breast cancer, in undiluted serum. The study involves the incorporation of interdigitated gold electrodes, which were used to prepare the electrochemical platform. A thiol terminated DNA aptamer with affinity for HER2 was used to prepare the bio-recognition layer via self-assembly on interdigitated gold surfaces. Non-specific binding was prevented by blocking free spaces on surface via starting block phosphate buffer saline-tween20 blocker. The sensor was characterized using cyclic voltammetry, electrochemical impedance spectroscopy (EIS), atomic force microscopy and contact angle studies. Non-Faradic EIS measurements were utilized to investigate the sensor performance via monitoring of the changes in capacitance. The aptasensor exhibited logarithmically detection of HER2 from 1pM to 100nM in both buffer and undiluted serum with limits of detection lower than 1pM. The results pave the way to develop other aptamer-based biosensors for protein biomarkers detection in undiluted serum., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Detection of malignant cells in tissue is a difficult hurdle in medical diagnostics and screening. Carbon nanotubes are extremely sensitive to their local environments, and nanotube-based field-effect transistors (NTFETs) provide a plethora of information regarding the mechanism of interaction with target analytes. Herein, we use a series of functionalized metal nanoparticle-decorated NTFET devices forming an array with multiple nonselective sensor units as the electronic "tongue", sensing all five basic tastes. By extraction of selected NTFET characteristics and using linear discriminant analysis, we have successfully detected and discriminated between malignant and nonmalignant tissues and cells. We also studied the sensing mechanism and what NTFET characteristics are responsible for the variation of response between cell types, allowing for the design of future studies such as detection of malignant cells in a biopsy or the effects of malignant cells on healthy tissue.

MicroRNAs (miRNAs) play crucial regulatory roles in various human diseases including cancer, making them promising biomarkers. However, given the low levels of miRNAs present in blood, their use as cancer biomarkers requires the development of simple and effective analytical methods. Herein, we report the development of a highly sensitive dual mode electrochemical platform for the detection of microRNAs. The platform was developed using peptide nucleic acids as probes on gold electrode surfaces to capture target miRNAs. A simple amplification strategy using gold nanoparticles has been employed exploiting the inherent charges of the nucleic acids. Electrochemical impedance spectroscopy was used to monitor the changes in capacitance upon any binding event, without the need for any redox markers. By using thiolated ferrocene, a complementary detection mode on the same sensor was developed where the increasing peaks of ferrocene were recorded using square wave voltammetry with increasing miRNA concentration. This dual-mode approach allows detection of miRNA with a limit of detection of 0.37 fM and a wide dynamic range from 1 fM to 100 nM along with clear distinction from mismatched target miRNA sequences. The electrochemical platform developed can be easily expanded to other miRNA/DNA detection along with the development of microarray platforms.

Because the transition from oxidative phosphorylation to anaerobic glycolytic metabolism is a hallmark of cancer progression, approaches to identify single living cancer cells by their unique glucose metabolic signature would be useful. Here, we present nanopipettes specifically developed to measure glucose levels in single cells with temporal and spatial resolution, and we use this technology to verify the hypothesis that individual cancer cells can indeed display higher intracellular glucose levels. The nanopipettes were functionalized as glucose nanosensors by immobilizing glucose oxidase (GOx) covalently to the tip so that the interaction of glucose with GOx resulted in a catalytic oxidation of β-d-glucose to d-gluconic acid, which was measured as a change in impedance due to drop in pH of the medium at the nanopipette tip. Calibration studies showed a direct relationship between impedance changes at the tip and glucose concentration in solution. The glucose nanosensor quantified single cell intracellular glucose levels in human fibroblasts and the metastatic breast cancer lines MDA-MB-231 and MCF7 and revealed that the cancer cells expressed reproducible and reliable increases in glucose levels compared to the nonmalignant cells. Nanopipettes allow repeated sampling of the same cell, as cells remain viable during and after measurements. Therefore, nanopipette-based glucose sensors provide an approach to compare changes in glucose levels with changes in proliferative or metastatic state. The platform has great promise for mechanistic investigations, as a diagnostic tool to distinguish cancer cells from nonmalignant cells in heterogeneous tissue biopsies, as well as a tool for monitoring cancer progression in situ.