Feasibility in the development of a multi-marker detection platform

Chronopotentiometric Nanopore Sensor Based on a Stimulus-Responsive Molecularly Imprinted Polymer for Label-Free Dual-Biomarker Detection

The development of sensors for detection of biomarkers exhibits an exciting potential in diagnosis of diseases. Herein, we propose a novel electrochemical sensing strategy for label-free dual-biomarker detection, which is based on the combination of stimulus-responsive molecularly imprinted polymer (MIP)-modified nanopores and a polymeric membrane chronopotentiometric sensor. The ion fluxes galvanostatically imposed on the sensing membrane surface can be blocked by the recognition reaction between the target biomarker in the sample solution and the stimulus-responsive MIP receptor in the nanopores, thus causing a potential change. By using two external stimuli (i.e., pH and temperature), the recognition abilities of the stimulus-responsive MIP receptor can be effectively modulated so that dual-biomarker label-free chronopotentiometric detection can be achieved. Using alpha fetoprotein (AFP) and prostate-specific antigen (PSA) as model biomarkers, the proposed sensor offers detection limits of 0.17 and 0.42 ng/mL for AFP and PSA, respectively.

Millimeter-scale magnetic implants paired with a fully integrated wearable device for wireless biophysical and biochemical sensing

Implantable sensors can directly interface with various organs for precise evaluation of health status. However, extracting signals from such sensors mainly requires transcutaneous wires, integrated circuit chips, or cumbersome readout equipment, which increases the risks of infection, reduces biocompatibility, or limits portability. Here, we develop a set of millimeter-scale, chip-less, and battery-less magnetic implants paired with a fully integrated wearable device for measuring biophysical and biochemical signals. The wearable device can induce a large amplitude damped vibration of the magnetic implants and capture their subsequent motions wirelessly. These motions reflect the biophysical conditions surrounding the implants and the concentration of a specific biochemical depending on the surface modification. Experiments in rat models demonstrate the capabilities of measuring cerebrospinal fluid (CSF) viscosity, intracranial pressure, and CSF glucose levels. This miniaturized system opens the possibility for continuous, wireless monitoring of a wide range of biophysical and biochemical conditions within the living organism.

Advanced Self-Powered Biofuel Cells with Capacitor and Nanogenerator for Biomarker Sensing

Self-powered biofuel cells (BFCs) have evolved for highly sensitive detection of biomarkers such as noncodon micro ribonucleic acids (miRNAs) in the presence of interfering substrates. Self-charging supercapacitive BFCs for in vivo and in vitro cellular microenvironments represent the most prevalent sensing mechanism for diagnosis. Therefore, self-powered biosensing (SPB) with a capacitor and contact separation with a triboelectric nanogenerator (TENG) offers electrochemical and colorimetric dual-mode detection via improved electrical signal intensity. In this review, we discuss three major components: stretchable self-powered BFC design, miRNA sensing, and impedance spectroscopy. A specific focus is given to 1) assembling of sensors for biomarkers, 2) electrical output signal intensification, and 3) role of supercapacitors and nanogenerators in SPBs. We outline the key features of stretchable SPBs and the sequence of miRNA sensing by SPBs. We have emphasized the need of a supercapacitor and nanogenerator for SPBs in the context of advanced assembly of the sensing unit. Finally, we outline the role of impedance spectroscopy in the detection and estimation of biomarkers. We highlight key challenges in SPBs for biomarker sensing, which needs improved sensing accuracy, integration strategies of electrochemical biosensing for in vitro and in vivo microenvironments, and the impact of miRNA sensing on cancer diagnostics. This article attempts a specific focus on the accuracy and limitations of sensing unit for miRNA biomarkers and associated tool for boosting electrical signal intensity for a potential big step further.

Magnetite azolla impedimetric nanobiosensor for phthalic acid esters quantification

Phthalic acid esters (PAEs) are a group of organic compounds that show vulnerability effects in different stages of human development. In this work, two sensitive and efficient impedimetric biosensors (IBs) were introduced and their interactions with four PAEs, namely dibutyl phthalate (DBP), dimethyl phthalate (DMP), di(2-ethylhexyl) phthalate (DEHP), and dicyclohexyl phthalate (DCHP), in aqueous solutions with these biosensors were separately investigated via electrochemical impedance spectroscopy (EIS). The surface of a copper electrode was modified by azolla fern dried powder (AZ) and magnetite-modified azolla nanocomposites (MAZ NCs) to form an azolla-based impedimetric biosensor (AZIB) and magnetite azolla nanocomposite-based impedimetric nanobiosensor (MAZIB), respectively. Determinations of PAEs with the designed biosensors were conducted based on their blocking effect on the biosensor surface to ferrous ions oxidation. After each impedimetric measurement, the electrode surface was covered again with the modifier. Nyquist plots were obtained and indicated that the charge-transfer resistance (R_CT) values of the bare electrode, AZIB, and MAZIB without injection of PAEs were 468.8, 438.7, and 285.1 kΩ, respectively. After the separate injection of DBP, DMP, DEHP, and DCHP (3 μg L^-1) on the surface of AZIB and MAZIB, R_CT values were obtained as 563.9, 588.5, 548.7, and 570.1 kΩ for AZIB and 878.2, 1219.2, 754.3, and 814.7 kΩ for MAZIB, respectively. It was observed that the PAE blockers with a smaller structure provided better point-by-point coverage of the surface, which led to a bigger shift in R_CT. The linear relationship between the EIS responses and each PAE concentration was investigated in the range of 0.1-1000 μg L^-1. The limit of detection (LOD) and limit of quantification (LOQ) values were obtained in the ranges of 0.003-0.005 μg L^-1 and 0.010-0.016 μg L^-1 for AZIB and 0.008-0.009 μg L^-1 and 0.027-0.031 μg L^-1 for MAZIB, respectively. The results showed that these biosensors can be used to determine PAEs in real aqueous samples with good relative recoveries ranging from 93.0-97.7% (RSD < 2.58%) for AZIB and 93.3-99.3% (RSD < 2.45%) for MAZIB. The results confirmed that these impedimetric biosensors offer high sensitivity and performance for the determination of trace PAEs in aqueous samples.

Faradaic electrochemical impedance spectroscopy for enhanced analyte detection in diagnostics

Electrochemical impedance spectroscopy (EIS) is a widely implementable technique that can be applied to many fields, ranging from disease detection to environmental monitoring. EIS as a biosensing tool allows detection of a broad range of target analytes in point-of-care (POC) and continuous applications. The technique is highly suitable for multimarker detection due to its ability to produce specific frequency responses depending on the target analyte and molecular recognition element (MRE) combination. EIS biosensor development has shown promising results for the medical industry in terms of diagnosis and prognosis for various biomarkers. EIS sensors offer a cost-efficient system and rapid detection times using minimal amounts of sample volumes, while simultaneously not disturbing the sample being studied due to low amplitude perturbations. These properties make the technique highly sensitive and specific. This paper presents a review of EIS biosensing advancements and introduces different detection techniques and MREs. Additionally, EIS's underlying theory and potential surface modification techniques are presented to further demonstrate the technique's ability to produce stable, specific, and sensitive biosensors.

Direct Measurement of a Biomarker's Native Optimal Frequency with Physical Adsorption Based Immobilization

The optimal frequency (OF) of a biomarker in electrochemical impedance spectroscopy (EIS) is the frequency at which the EIS response best reflects the binding of the biomarker to its molecular recognition element. Commonly, biosensors rely on complicated immobilization chemistry to attach biological molecules to the sensor surface, making the direct study of a biomarker's native OF a challenge. Physical adsorption presents a simple immobilization strategy to study the native biomarker's OF, but its utility is often discouraged due to a loss in biological activity. To directly study a biomarker's native OF and investigate the potential of OF to overcome the limitations of physical adsorption, a combination of EIS and glutaraldehyde-mediated physical adsorption was explored. The experimental sensing platform was prepared by immobilizing either anti-lactoferrin (Lfn) IgG or anti-immunoglobulin E (IgE) onto screen printed carbon electrodes. After characterizing the native OFs of both biomarkers, investigation of the platform's specificity, stability, and performance in complex medium was found to be sufficient. Finally, a paper-based tear sampling component was integrated to transform the testing platform into a prototypical point-of-care dry eye diagnostic. The investigation of native OFs revealed a correlation between the native OFs (57.44 and 371.1 Hz for Lfn and IgE, respectively) and the molecular weight of the antibody-antigen complex. Impedance responses at the native OFs have enabled detection limits of 0.05 mg/mL and 40 ng/mL for Lfn and IgE, respectively, covering the clinically relevant ranges. The native OFs were found to be robust across various testing mediums and conditions.

Lab-on-a-chip electrical multiplexing techniques for cellular and molecular biomarker detection

Signal multiplexing is vital to develop lab-on-a-chip devices that can detect and quantify multiple cellular and molecular biomarkers with high throughput, short analysis time, and low cost. Electrical detection of biomarkers has been widely used in lab-on-a-chip devices because it requires less external equipment and simple signal processing and provides higher scalability. Various electrical multiplexing for lab-on-a-chip devices have been developed for comprehensive, high throughput, and rapid analysis of biomarkers. In this paper, we first briefly introduce the widely used electrochemical and electrical impedance sensing methods. Next, we focus on reviewing various electrical multiplexing techniques that had achieved certain successes on rapid cellular and molecular biomarker detection, including direct methods (spatial and time multiplexing), and emerging technologies (frequency, codes, particle-based multiplexing). Lastly, the future opportunities and challenges on electrical multiplexing techniques are also discussed.

Enhancing Glycemic Control via Detection of Insulin Using Electrochemical Impedance Spectroscopy

BACKGROUND

Currently, glycemic management for individuals with diabetes mellitus involves monitoring glucose only, which is insufficient as glucose metabolism involves other biomarkers such as insulin. Monitoring additional biomarkers alongside glucose has been proposed to improve glycemic control. In this work, the development of a rapid and label-free insulin biosensor with high sensitivity and accuracy is presented. The insulin sensor prototype also serves as a prior study for a multimarker sensing platform technology that can further improve glycemic control in the future.

METHODS

Electrochemical impedance spectroscopy was used to identify an optimal frequency specific to insulin detection on a gold disk electrode with insulin antibody immobilized, which was accomplished by conjugating the primary amines of insulin antibody to the carboxylic bond of the self-assembling monolayer on the gold surface. After blocking with ethanolamine, the insulin physiological concentration gradient was tested. The imaginary impedance was correlated to insulin concentration and the results were compared with standard equivalent circuit analysis and correlation of charge transfer resistance to target concentration.

RESULTS

The optimal frequency of insulin is 810.5 Hz, which is characterized by having the highest sensitivity and sufficient specificity. The lower limit of detection was 2.26 [Formula: see text] which is comparable to a standard and better than traditional approaches.

CONCLUSION

An insulin biosensor prototype capable of detecting insulin in physiological range without complex data normalization was developed. This prototype will be the ground works of a multimarker platform sensor technology for future all-in-one glycemic management sensors.