Ultrasensitive Electrochemical Detection of Carcinoembryonic Antigen with a Label‐Free Immunosensor using Gold Nanoparticle‐Decorated Poly(pyrrole‐co‐3,4‐ethylenedioxythiophene)

Construction of Nonenzymatic Flexible Electrochemical Sensor for Glucose Using Bimetallic Copper Ferrite/Sulfur-Doped Graphene Oxide Water-Based Conductive Ink by Noninvasive Method

Diabetes is a chronic disease that results in elevated blood glucose levels due to insufficient insulin production by the pancreas or impaired insulin utilization by the body. The development of effective tools for the in vitro detection of blood glucose is of paramount importance. Flexible electrodes serve as indispensable components in point-of-care systems, thus increasing accessibility and personalization in health monitoring. We present the preparation of handmade screen-printed electrode with water-based conductive ink for in vitro nonenzymatic glucose (Glu) determination at physiological pH values. The investigation aimed to identify the optimal conditions for formulating and composing the conductive ink used to create a copper ferrite/sulfur-doped graphene oxide/graphite/screen-printed electrode (CuFe2O4/S-GO/G/SPE). The resulting CuFe2O4/S-GO/G/SPE shows excellent glucose sensing ability with a limit of detection (LOD) of 2.93 μM. The superior determination at physiological pH is attributed to the complex structure formed by CuFe2O4 nanoparticles with glucose molecules in the basic pH conductive ink structure. Additionally, the excellent delocalization and conductivity of the S-GO particles in this complex structure contribute to improved performance. The study on artificial sweat samples resulted in achieving recovery values of 96.60% to 104.97%. In conclusion, the nonenzymatic and noninvasive Glu sensor printed with conductive ink containing CuFe2O4/S-GO/G on a flexible paper substrate surface demonstrated remarkable capabilities for determining Glu levels in artificial sweat samples. SPEs prepared with conductive ink produced by using these materials are promising candidates for use as electrodes in flexible and wearable sensor technology.

Advanced laser-induced graphene-based electrochemical immunosensor for the detection of C-reactive protein

C-reactive protein (CRP) is a critical biomarker for detecting inflammation and forecasting cardiovascular disease. We present an advanced electrochemical immunosensor utilizing laser-induced graphene (LIG)/MXene-gold nanoparticles (Mx-AuNPs) electrode for CRP detection. The Mx-AuNPs nanocomposite, synthesized via in-situ reduction of HAuCl4 by MXene, leverages MXene's reducing properties for effective nanoparticle deposition, confirmed through scanning electron microscopy. This electrode demonstrates superior electrochemical performance due to enhanced surface area and synergy between LIG and Mx-AuNPs, improving overall electrode conductivity. The Anti-CRP antibody, immobilized via a cysteamine linker, enables CRP detection. The immunosensor achieves excellent detection across 10 pg mL-1 to 10 µg mL-1 CRP, with a low detection limit of 1.45 pg mL-1, and shows high selectivity for CRP. This LIG/Mx-AuNPs-based immunosensor is promising for sensitive CRP detection, aiding early cardiovascular disease diagnosis and improving patient outcomes.

Techniques for characterizing biofunctionalized surfaces for bioanalysis purposes

Surface biofunctionalization is an essential stage in the preparation of any bioassay affecting its analytical performance. However, a complete characterization of the biofunctionalized surface, considering studies of coverage density, distribution and orientation of biomolecules, layer thickness, and target biorecognition efficiency, is not met most of the time. This review is a critical overview of the main techniques and strategies used for characterizing biofunctionalized surfaces and the process in between. Emphasis is given to scanning force microscopies as the most versatile and suitable tools to evaluate the quality of the biofunctionalized surfaces in real-time dynamic experiments, highlighting the helpful of atomic force microscopy, Kelvin probe force microscopy, electrochemical atomic force microscopy and photo-induced force microscopy. Other techniques such as optical and electronic microscopies, quartz crystal microbalance, X-ray photoelectron spectroscopy, contact angle, and electrochemical techniques, are also discussed regarding their advantages and disadvantages in addressing the whole characterization of the biomodified surface. Scarce reviews point out the importance of practicing an entire characterization of the biofunctionalized surfaces. This is the first review that embraces this topic discussing a wide variety of characterization tools applied in any bioanalysis platform developed to detect both clinical and environmental analytes. This survey provides information to the analysts on the applications, strengths, and weaknesses of the techniques discussed here to extract fruitful insights from them. The aim is to prompt and help the analysts to accomplish an entire assessment of the biofunctionalized surface, and profit from the information obtained to enhance the bioanalysis output.

Bioreceptors' immobilization by hydrogen bonding interactions and differential pulse voltammetry for completely label-free electrochemical biosensors

Label-free electrochemical biosensors show great potential for the development of point-of-care devices (POCDs) for environmental and clinical applications. These sensors operate with shorter analysis times and are more economic than the labelled ones. Here, four completely label-free biosensors without electron transfer mediators were developed for hepatitis B virus (HBV) detection. The approach consisted in (i) the modification of gold surfaces with cysteamine (CT) or cysteine (CS) linkers, (ii) the subsequent antibody (Ab) immobilization, either directly by hydrogen bonding (HB) interactions or by covalent bonds (CB) using additional reagents, and (iii) measuring the biosensor response by electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The electrode surfaces at each stage of the modification process were characterised by X-ray photo-electron spectroscopy (XPS) and atomic force microscopy (AFM). The combination of Ab immobilization by HB with the DPV analysis displayed improved repeatability, lower interference to serum matrix and similar limits of detection and quantification than the traditional biosensors that immobilize the Ab via CB and use EIS as readout technique. The Ab immobilization by HB is shown as a simple, efficient and low-cost alternative to CB ones, while DPV was faster and showed better performance than EIS. The CT-HB biosensor displayed the lowest limits of detection and quantification of 0.14 and 0.46 ng/mL, respectively, a 0.46-12.5 ng/mL linear analytical range, and 100% of recovery for 1/10 human serum media during HBV surface antigen detection by DPV. Even, it preserved the initial sensing capability after 7 days of its fabrication.

Single laser synthesis of gold nanoparticles-polypyrrole-chitosan on laser-induced graphene for ascorbic acid detection

The simultaneous synthesis of gold nanoparticles (AuNPs) and graphene by laser ablation was demonstrated. The in-situ synthesis was performed by laser ablation of a polymer substrate covered with a gold precursor dispersion. The gold precursor was prepared in a copolymer solution of pyrrole (Py) and chitosan (Chi) to improve the nucleation of gold embedded on the laser-induced graphene electrode (LIGE). The morphology of AuNPs-pPy-Chi/LIGE was studied by scanning electron microscopy and characterized electrochemically by cyclic voltammetry. A comprehensive investigation of the electrochemical and physical features of the AuNPs-pPy-Chi/LIGE was carried out. The parameters of differential pulse voltammetry were adjusted to enhance the response to ascorbic acid (AA). The AuNPs-pPy-Chi/LIGE produced two linear ranges: from 0.25 to 5.00 and 5.00-25.00 mmol L-1. The limit of detection was 0.22 mmol L-1. Hundreds of electrodes were tested to demonstrate the excellent reproducibility of the AuNPs-pPy-Chi/LIGE fabrication. Overall, the proposed electrode allows the successful detection of AA in orange juice products with acceptable accuracy (recoveries = 97 ± 2 to 109.1 ± 0.7). The preparation strategy of the proposed AuNPs-pPy-Chi/LIGE could be adapted to detect other compounds or biomarkers.

Synthesis of flower-like ZnO nanoparticles for label-free point of care detection of carcinoembryonic antigen

In this work, flower-like ZnO nanoparticles (ZnONPs) were synthesized using zinc nitrate (Zn(NO3)2 6H2O) as a precursor with KOH. The morphology of the ZnONPs was controlled by varying the synthesis temperature at 50, 75 and 95 °C. The morphology and structure of ZnONPs were characterized using Scanning Electron Microscopy, and X-Ray Diffraction and Brunauer-Emmett Teller analysis. ZnONPs were successfully synthesized by a simple chemical precipitation method. A synthesis temperature of 75 °C produced the most suitable flower-like ZnONPs, which were combined with graphene nanoplatelets to develop a label-free electrochemical immunosensor for the detection of the colon cancer biomarker carcinoembryonic antigen in human serum. Under optimum conditions, the developed immunosensor showed a linear range of 0.5-10.0 ng mL-1 with a limit of detection of 0.44 ng mL-1. The label-free electrochemical immunosensor exhibited good selectivity, reproducibility, and repeatability, and recoveries were excellent. The immunosensor is used with a Near-Field Communication potentiostat connected to a smartphone to facilitate point-of-care cancer detection in low-resource locations.

Label-Free Immunosensor Based on Polyaniline-Loaded MXene and Gold-Decorated β-Cyclodextrin for Efficient Detection of Carcinoembryonic Antigen

Multiple strategies have been employed to improve the performance of label-free immunosensors, among which building highly conductive interfaces and introducing suitable biocompatible carriers for immobilizing antibodies or antigens are believed to be efficient in most cases. Inspired by this, a label-free immunosensor for carcinoembryonic antigen (CEA) detection was constructed by assembling AuNPs and β-CD (Au-β-CD) on the surface of FTO modified with PANI-decorated f-MXene (MXene@PANI). Driven by the high electron conductivity of MXene@PANI and the excellent capability of Au-β-CD for antibody immobilization, the BSA/anti-CEA/Au-β-CD/MXene@PANI/FTO immunosensor exhibits balanced performance towards CEA detection, with a practical linear range of 0.5–350 ng/mL and a low detection limit of 0.0429 ng/mL. Meanwhile, the proposed sensor presents satisfying selectivity, repeatability, and stability, as well as feasibility in clinic serum samples. This work would enlighten the prospective research on the alternative strategies in constructing advanced immunosensors.