Electrical Biosensors Research Articles

Integrated Platform Addressing the Finger-Prick Blood Processing Challenges of Point-of-Care Electrical Biomarker Testing.

Continued advances in label-free electrical biosensors pave the way to simple, rapid, cost-effective, high-sensitivity, and quantitative biomarker testing at the point-of-care setting that would profoundly transform healthcare. However, implementation in routine diagnostics is faced with significant challenges associated with the inherent requirement for biofluid sample processing before and during testing. We present here a simple yet robust autonomous finger-prick blood sample processing platform integrated with nanoscale field-effect transistor biosensors and demonstrate the feasibility of measuring the SARS-CoV-2 nucleocapsid protein. The 3D-printed platform incorporates a high-yield blood-to-plasma separation module and a delay valve designed to terminate the assay at a specific time. The platform is driven by hydrostatic pressure to efficiently and automatically dispense plasma and washing/measurement buffer to the nanosensors. Our model study demonstrates the feasibility of detecting down to 1.4 pg/mL of the SARS-CoV-2 nucleocapsid protein within 25 min and with only minimal operator intervention.

A pretreatment-free electrical capacitance biosensor for exosome detection in undiluted serum

The exosome is considered a useful biomarker for the early diagnosis of cancer. However, pretreatment of samples used in diagnosis is time-consuming. Herein, we fabricated a capacitance-based electrical biosensor that requires no pretreatment of the sample; it is composed of a DNA aptamer/molybdenum disulfide (MoS2) heterolayer on an interdigitated micro-gap electrode (IDMGE)/printed circuit board (PCB) system for detecting exosomes in an undiluted serum sample. The DNA aptamer detects the CD63 protein on the exosome as the biomarker, while the MoS2 nanoparticle enhances electrical sensitivity. In this study, for the first time, the IDMGE system was used to amplify the electrical signal efficiently for exosome detection. The IDMGE amplifies the capacitance signal as the gap between electrodes decreases, making it easy to detect the target by utilizing the heightened sensitivity. Moreover, it is possible to immobilize a bio-probe more efficiently than with an electrical sensitivity–enhancing electrode with the same area. The thiol-modified (SH-) CD63 DNA aptamer was introduced as the bio-probe that selectively binds to the CD63 protein on the exosome surface. The capacitance signal from the IDMGE electrical sensor increased linearly with the increase in the concentration of exosomes in human serum expressed on a logarithmic scale, the detection limit being 2192.6 exosomes/mL. The proposed biosensor can detect exosomes in undiluted human serum with high selectivity and sensitivity. A blind test was also carried out to test the reliability of the biosensor. The capacitance-based electrical biosensor thus offers a new platform for cancer diagnosis in the future.

Distinct classes of potassium channels fused to GPCRs as electrical signaling biosensors

SummaryLigand-gated ion channels (LGICs) are natural biosensors generating electrical signals in response to the binding of specific ligands. Creating de novo LGICs for biosensing applications is technically challenging. We have previously designed modified LGICs by linking G protein-coupled receptors (GPCRs) to the Kir6.2 channel. In this article, we extrapolate these design concepts to other channels with different structures and oligomeric states, namely a tetrameric viral Kcv channel and the dimeric mouse TREK-1 channel. After precise engineering of the linker regions, the two ion channels were successfully regulated by a GPCR fused to their N-terminal domain. Two-electrode voltage-clamp recordings showed that Kcv and mTREK-1 fusions were inhibited and activated by GPCR agonists, respectively, and antagonists abolished both effects. Thus, dissimilar ion channels can be allosterically regulated through their N-terminal domains, suggesting that this is a generalizable approach for ion channel engineering.

Real-Time Monitoring of Dissection Events of Single Budding Yeast in a Microfluidic Cell-Culturing Device Integrated With Electrical Impedance Biosensor.

Microfluidic devices in combination with fluorescent microscopy offer high-resolution and high-content platforms to study single-cell morphology, behavior and dynamic process in replicative aging of budding yeast, Saccharomyces cerevisiae. However, a huge mass of recorded images makes the data processing labor-intensive and time-consuming to determine yeast replicative lifespan (RLS), a primary criterion in yeast aging. To address this limitation and pursue label-free RLS assays, electrical impedance spectroscopy (EIS) that can be easily functionalized through microelectrodes in microfluidic devices, was introduced to monitor cell growth and division of budding yeast. Herein, a microfluidic device integrated with EIS biosensor was proposed to perform in-situ impedance measurement of yeast proliferation in single-cell resolution so as to identify the momentary events of daughter dissection from its mother. Single yeast cells were reliably immobilized at the bottleneck-like traps for continuous culturing, during which daughter cells were effectively detached from their mother cells by hydraulic shear forces. Time-lapse impedance measurement was performed every 2 min to monitor the cellular process including budding, division and dissection. By using the K-means clustering algorithm to analyze a self-defined parameter “Dissection Indicator,” to our knowledge for the first time, the momentary event of a daughter removing from its mother cell was accurately extracted from EIS signals. Thus, the identification of daughter dissection events based on impedance sensing technology has been validated. With further development, this microfluidic device integrated with electrical impedance biosensor holds promising applications in high-throughput, real-time and label-free analysis of budding yeast aging and RLS.

A Review of Advanced Impedance Biosensors with Microfluidic Chips for Single-Cell Analysis.

Electrical impedance biosensors combined with microfluidic devices can be used to analyze fundamental biological processes for high-throughput analysis at the single-cell scale. These specialized analytical tools can determine the effectiveness and toxicity of drugs with high sensitivity and demonstrate biological functions on a single-cell scale. Because the various parameters of the cells can be measured depending on methods of single-cell trapping, technological development ultimately determine the efficiency and performance of the sensors. Identifying the latest trends in single-cell trapping technologies afford opportunities such as new structural design and combination with other technologies. This will lead to more advanced applications towards improving measurement sensitivity to the desired target. In this review, we examined the basic principles of impedance sensors and their applications in various biological fields. In the next step, we introduced the latest trend of microfluidic chip technology for trapping single cells and summarized the important findings on the characteristics of single cells in impedance biosensor systems that successfully trapped single cells. This is expected to be used as a leading technology in cell biology, pathology, and pharmacological fields, promoting the further understanding of complex functions and mechanisms within individual cells with numerous data sampling and accurate analysis capabilities.

Design of a bioelectronic tongue for glucose monitoring using zinc oxide nanofibers and graphene derivatives

Monitoring glucose levels is critical for diabetes management and might be a key step in the development of individualized treatment strategies. In this scenario, tracking salivary glucose has been recognized as a promising strategy due to its merits of ease sampling and non-invasive nature. In this paper, we report on the development of an electrical impedance-based biosensor array to distinguish glucose at different concentrations in saliva. The enzymatic biosensors were made of gold interdigitated electrodes coated with pristine electrospun zinc oxide nanofibers (NFZ) and NFZ combined with graphene-based nanomaterials (i.e., reduced graphene oxide - rGO and graphene quantum dots - GQDs), on which a layer of glucose oxidase (GOx) enzyme was adsorbed. Electrical impedance measurements indicate that the NFZ-GQDs@GOx and NFZ-rGO@GOx platforms presented good linear relationship with glucose concentration in the range of 0.1 to 6 mM. The highest sensitivity was reached for NFZ-rGO@GOx with a detection limit (LOD) of 14 μM, while the LOD was 32 μM for NFZ-GQDs@GOx. Both biosensors were also capable of detecting glucose in artificial saliva using aliquots of 10 μL, with recovery between 87.3 and 106.8%. Furthermore, the three sensing units (NFZ@GOx, NFZ-rGO@GOx and NFZ-GQDs@GOx) were employed to build a bioelectronic tongue. Using Principal Component Analysis (PCA) technique to project the electrical impedance data of all sensing units allowed the discrimination of the different glucose concentrations and interferents. This study reveals the applicability of the developed bioelectronic tongue as non-invasive glucose sensors, which approach could also be pottentially adapted to detect other disease biomarkers present in saliva.

A Rapid Detection of COVID-19 Viral RNA in Human Saliva Using Electrical Double Layer-Gated Field-Effect Transistor-Based Biosensors.

In light of the swift outspread and considerable mortality, coronavirus disease 2019 (COVID‐19) necessitates a rapid screening tool and a precise diagnosis. Saliva is considered as an alternative specimen to detect the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) since the viral load is comparable to what are found in a throat and a nasal cavity. The electrical double layer (EDL)‐gated field‐effect transistor‐based biosensor (BioFET) emerges as a promising candidate for salivary COVID‐19 tests due to a high sensitivity, a portable configuration, a label‐free operation, and a matrix insensitivity. In this work, the authors utilize EDL‐gated BioFETs to detect complementary DNAs (cDNAs) and viral RNAs with various testing conditions such as switches of probes, temperature treatments, and matrices. The selectivity is confirmed with cDNA and noncomplementary DNA (ncDNA), exhibiting an eightfold difference in electrical signals. The matrix insensitivity is evaluated, and BioFETs successfully validate the detection of SARS‐CoV‐2 N‐gene RNA down to 1 fm in diluted human saliva with a 95°C‐ and a 25°C‐treatment, respectively. This proposed system has a high potential to be deployed for an on‐site COVID‐19 screening, improving the disease control and benefitting frontline healthcare system.

Tuning Electrostatic Gating of Semiconducting Carbon Nanotubes by Controlling Protein Orientation in Biosensing Devices.

The ability to detect proteins through gating conductance by their unique surface electrostatic signature holds great potential for improving biosensing sensitivity and precision. Two challenges are: (1) defining the electrostatic surface of the incoming ligand protein presented to the conductive surface; (2) bridging the Debye gap to generate a measurable response. Herein, we report the construction of nanoscale protein‐based sensing devices designed to present proteins in defined orientations; this allowed us to control the local electrostatic surface presented within the Debye length, and thus modulate the conductance gating effect upon binding incoming protein targets. Using a β‐lactamase binding protein (BLIP2) as the capture protein attached to carbon nanotube field effect transistors in different defined orientations. Device conductance had influence on binding TEM‐1, an important β‐lactamase involved in antimicrobial resistance (AMR). Conductance increased or decreased depending on TEM‐1 presenting either negative or positive local charge patches, demonstrating that local electrostatic properties, as opposed to protein net charge, act as the key driving force for electrostatic gating. This, in turn can, improve our ability to tune the gating of electrical biosensors toward optimized detection, including for AMR as outlined herein.

Tuning Electrostatic Gating of Semiconducting Carbon Nanotubes by Controlling Protein Orientation in Biosensing Devices.

The ability to detect proteins through gating conductance by their unique surface electrostatic signature holds great potential for improving biosensing sensitivity and precision. Two challenges are: (1) defining the electrostatic surface of the incoming ligand protein presented to the conductive surface; (2) bridging the Debye gap to generate a measurable response. Herein, we report the construction of nanoscale protein-based sensing devices designed to present proteins in defined orientations; this allowed us to control the local electrostatic surface presented within the Debye length, and thus modulate the conductance gating effect upon binding incoming protein targets. Using a β-lactamase binding protein (BLIP2) as the capture protein attached to carbon nanotube field effect transistors in different defined orientations. Device conductance had influence on binding TEM-1, an important β-lactamase involved in antimicrobial resistance (AMR). Conductance increased or decreased depending on TEM-1 presenting either negative or positive local charge patches, demonstrating that local electrostatic properties, as opposed to protein net charge, act as the key driving force for electrostatic gating. This, in turn can, improve our ability to tune the gating of electrical biosensors toward optimized detection, including for AMR as outlined herein.

Two-Dimensional Material-Based Colorimetric Biosensors: A Review.

Two-dimensional (2D) materials such as graphene, graphene oxide, transition metal oxide, MXene and others have shown high potential for the design and fabrication of various sensors and biosensors due to their 2D layered structure and unique properties. Compared to traditional fluorescent, electrochemical, and electrical biosensors, colorimetric biosensors exhibit several advantages including naked-eye determination, low cost, quick response, and easy fabrication. In this review, we present recent advances in the design, fabrication, and applications of 2D material-based high-performance colorimetric biosensors. Potential colorimetric sensing mechanisms and optimal material selection as well as sensor fabrication are introduced in brief. In addition, colorimetric biosensors based on different 2D materials such as graphene, transition metal dichalcogenide/oxide, MXenes, metal–organic frameworks, and metal nanoplates for the sensitive detection of DNA, proteins, viruses, small molecules, metallic ions, and others are presented and discussed in detail. This work will be helpful for readers to understand the knowledge of 2D material modification, nanozymes, and the synthesis of hybrid materials; meanwhile, it could be valuable to promote the design, fabrication, and applications of 2D material-based sensors and biosensors in quick bioanalysis and disease diagnostics.

Benchmarking Electrolyte‐Gated Monolayer MoS2 Field‐Effect Transistors in Aqueous Environments

Most electrical sensor and biosensor elements require reliable transducing elements to convert small potential changes into easy to read out current signals. Offering inherent signal magnification and being operable in many relevant environments field‐effect transistors (FETs) are the element of choice in many cases. In particular, using electrolyte gating, numerous sensors and biosensors have been realized in aqueous environments. Over the past years, electrolyte‐gated FETs have been fabricated using a variety of semiconducting materials, including graphene, ZnO, as well as conjugated molecules and polymers. Above all, using conducting polymers top‐performing devices have been achieved. Herein, an approach to use a transition metal dichalcogenide (TMDC)‐based monolayer device as a transducing element is presented. Using MoS2 monolayers, it is shown that such electrolyte‐gated devices may be regarded as very promising transducing elements for sensor and biosensor applications, enabled by their high sensitivity for environmental changes and the possibility of using the naturally occurring sulfur vacancies as grafting points of biorecognition layers. Furthermore, the behavior of such a device under prolonged operation in a dilute biologically relevant electrolyte such as phosphate buffered saline solution (PBS) is reported.

Infection-Mediated Clinical Biomarkers for a COVID-19 Electrical Biosensing Platform.

The race towards the development of user-friendly, portable, fast-detection, and low-cost devices for healthcare systems has become the focus of effective screening efforts since the pandemic attack in December 2019, which is known as the coronavirus disease 2019 (COVID-19) pandemic. Currently existing techniques such as RT-PCR, antigen–antibody-based detection, and CT scans are prompt solutions for diagnosing infected patients. However, the limitations of currently available indicators have enticed researchers to search for adjunct or additional solutions for COVID-19 diagnosis. Meanwhile, identifying biomarkers or indicators is necessary for understanding the severity of the disease and aids in developing efficient drugs and vaccines. Therefore, clinical studies on infected patients revealed that infection-mediated clinical biomarkers, especially pro-inflammatory cytokines and acute phase proteins, are highly associated with COVID-19. These biomarkers are undermined or overlooked in the context of diagnosis and prognosis evaluation of infected patients. Hence, this review discusses the potential implementation of these biomarkers for COVID-19 electrical biosensing platforms. The secretion range for each biomarker is reviewed based on clinical studies. Currently available electrical biosensors comprising electrochemical and electronic biosensors associated with these biomarkers are discussed, and insights into the use of infection-mediated clinical biomarkers as prognostic and adjunct diagnostic indicators in developing an electrical-based COVID-19 biosensor are provided.

Novel electronic biosensor for automated inoculum preparation to accelerate antimicrobial susceptibility testing

A key predictor of morbidity and mortality for patients with a bloodstream infection is time to appropriate antimicrobial therapy. Accelerating antimicrobial susceptibility testing from positive blood cultures is therefore key to improving patient outcomes, yet traditional laboratory approaches can require 2–4 days for actionable results. The eQUANT—a novel instrument utilizing electrical biosensors—produces a standardized inoculum equivalent to a 0.5 McFarland directly from positive blood cultures. This proof-of-concept study demonstrates that eQUANT inocula prepared from clinically significant species of Enterobacterales were comparable to 0.5 McF inocula generated from bacterial colonies in both CFU/ml concentration and performance in antimicrobial susceptibility testing, with ≥ 95% essential and categorical agreement for VITEK2 and disk diffusion. The eQUANT, combined with a rapid, direct from positive blood culture identification technique, can allow the clinical laboratory to begin antimicrobial susceptibility testing using a standardized inoculum approximately 2–3 h after a blood culture flags positive. This has the potential to improve clinical practice by accelerating conventional antimicrobial susceptibility testing and the resulting targeted antibiotic therapy.

Electrical biosensing with synthetic nanopores and nanochannels

The integration of constriction structures such as nanopores and nanochannels into fluidic devices discloses powerful biosensing capabilities that can be tuned to a wide range of analytes through conceptually simple size calibrations. The practical implementation of this tuning requires a nontrivial manipulation of matter at nanoscale with further requirements for low complexity and low-cost procedures that may be adapted to industrial production. Here, we review the recent progress on the fabrication techniques of nanopores and nanochannels, together with the efforts to realize their full biosensing potential by understanding and amending the problems still afflicting the measurement performed during operation. • Confining fluidic nanostructures provide single-molecule sensitivity to biosensors. • Crucial tuning of nanostructure size stimulates the research on fabrication. • D materials boost the performance of nanopore technology. • Polymeric nanochannels pave the way for high-throughput applications in biosensing.

Subtle Application of Electrical Field-Induced Lossy Mode Resonance to Enhance Performance of Optical Planar Waveguide Biosensor.

Many studies concern the generation of lossy mode resonances (LMRs) using metallic oxide thin films that are deposited on optical fiber. However, the LMR-based optical fiber sensors are frangible, do not allow easy surface modification, and are not suited to mass production. This study proposes an electrical field-induced LMR-based biosensor with an optical planar waveguide to replace surface modification and allow the mass production of protein biosensors and accelerate the speed of the analyte to decrease the detection time. Experimentally, the biosensor is evaluated using charged serum albumin molecules and characterized in terms of the LMR wavelength shift using an externally applied voltage for different durations. The externally applied voltage generates a significant electric field, which drives the non-neutralized biomolecules and increases the LMR wavelength shift. Our experimental results demonstrate that there are two different mechanisms of adsorption of serum albumin molecules for short-term and long-term observations. These are used to calculate the sensitivity of the biosensor. This electrical field-induced method is highly significant for the development and fabrication of LMR-based biosensors.

Carbon-Dot-Enhanced Graphene Field-Effect Transistors for Ultrasensitive Detection of Exosomes.

Graphene field-effect transistors (GFETs) are suitable building blocks for high-performance electrical biosensors, because graphene inherently exhibits a strong response to charged biomolecules on its surface. However, achieving ultralow limit-of-detection (LoD) is limited by sensor response time and screening effect. Herein, we demonstrate that the detection limit of GFET biosensors can be improved significantly by decorating the uncovered graphene sensor area with carbon dots (CDs). The developed CDs-GFET biosensors used for exosome detection exhibited higher sensitivity, faster response, and three orders of magnitude improvements in the LoD compared with nondecorated GFET biosensors. A LoD down to 100 particles/μL was achieved with CDs-GFET sensor for exosome detection with the capability for further improvements. The results were further supported by atomic force microscopy (AFM) and fluorescent microscopy measurements. The high-performance CDs-GFET biosensors will aid the development of an ultrahigh sensitivity biosensing platform based on graphene for rapid and early diagnosis of diseases.

A review on application of ZnO nano particles as biosensors

Recently some of the metal nano composites are used in the semiconductor based electrical, electrochemical and optical bio-sensors. ZnO nano particles have drawn great interest due to its unique properties like low cost, wide range of band gap, biocompatible, easy to synthesize in different size and shapes and catalytic surface activity. The surface of the ZnO nano particles are perfect for immobilisation of bio molecules without hampering their biological activity. This property increase the sensitivity of bio-sensors. In this review we highlight the use of different ZnO nano particles in bio-sensors enhancing the efficiency of Bio-sensors.

Soft and flexible gold microelectrodes by supersonic cluster beam deposition and femtosecond laser processing

Soft and flexible microelectrodes are fabricated and patterned in a novel approach integrating supersonic cluster beam deposition (SCBD) of gold nanoparticles onto Polydimethylsiloxane (PDMS) followed by femtosecond (fs) laser processing. SCBD of gold nanoparticles in PDMS forms a nanocomposite film with mechanical properties similar to those of the elastomeric substrate. Electrically neutral metallic nanoparticles penetrate the polymeric matrix and distribute randomly up to a depth of a few hundred nanometers forming a path of ohmic conduction. High resolution patterning on soft substrates is a major challenge that was overcome by femtosecond laser ablation of micrometer lines with relatively very little thermal damage. Microelectrodes were fabricated with a width down to 3 μm. The printed metal line sheet resistance was 480 Ohm/square for the 100 nm thick film and 210 Ohm/square for the 200 nm thick film. The calculated average film specific resistivity was found to be 2.5–2.6mΩ·cm. It is ~3 orders of magnitude higher than that of physical vapor deposited gold; therefore, it is not suitable for high current interconnects but sufficient for low-current signal transmission such as for electrical and electrochemical biosensors.

Biosensors Based on Mechanical and Electrical Detection Techniques.

Biosensors are powerful analytical tools for biology and biomedicine, with applications ranging from drug discovery to medical diagnostics, food safety, and agricultural and environmental monitoring. Typically, biological recognition receptors, such as enzymes, antibodies, and nucleic acids, are immobilized on a surface, and used to interact with one or more specific analytes to produce a physical or chemical change, which can be captured and converted to an optical or electrical signal by a transducer. However, many existing biosensing methods rely on chemical, electrochemical and optical methods of identification and detection of specific targets, and are often: complex, expensive, time consuming, suffer from a lack of portability, or may require centralised testing by qualified personnel. Given the general dependence of most optical and electrochemical techniques on labelling molecules, this review will instead focus on mechanical and electrical detection techniques that can provide information on a broad range of species without the requirement of labelling. These techniques are often able to provide data in real time, with good temporal sensitivity. This review will cover the advances in the development of mechanical and electrical biosensors, highlighting the challenges and opportunities therein.

Adsorption behavior of guanine, adenine, thymine, and cytosine nucleobases of DNA on zinc oxide-graphene nanosensor: A DFT study

In this paper, we studied the guanine, adenine, thymine, and cytosine as based DNA nucleotides adsorption over Zinc oxide decorated on graphene sheet (ZnO-GS). The stability, the adsorption mechanism, density of states (DOS) and the change of electrical conductivity properties are investigated. All calculations were performed on the basis of Density Functional Theory using Quantum espresso package and BoltzTrap code. The results of the studies showed that ZnO-GS nanostructure as compared with GS has high potential for DNA detection. The energy for adsorption of G, A, T and C on ZnO-GS was 1.70, 1.58, 1.46 and 1.43 eV, respectively (G>A>T>C). The energy of DNA adsorption on ZnO-GS was calculated to be 50 % higher than the graphene. The results of the electrical conductivity change also indicate that the change in electrical conductivity for ZnO-GS occurs in the range from −0.1 eV to +0.1 eV, which is more than twice the conductivity change due to the adsorption of DNA on GS. As a result, the ZnO-GS nanostructure can be used as an electrical biosensor to detect DNA by changing electrical conductivity property. On this basis, it can be concluded that the electrical conductivity is created in ZnO due to the adsorption of DNA by ZnO-GS and strengthens electron transfer by GS, which is also the result of the energy adsorption calculations. Therefore, the ZnO-GS nanostructure, as compared with GS, transmits more current in less time between DNA and electrode surface. This change in behavior is consistent with the results reported by experimental studies.