Separation/Concentration-signal-amplification in-One Method Based on Electrochemical Conversion of Magnetic Nanoparticles for Electrochemical Biosensing

Portable Detection of Copper Ion Using Personal Glucose Meter

A simple and sensitive method for Cu2+ detection was developed using the Cu+-catalyzed alkyne-azide cycloaddition reaction, Fe3O4 magnetic nanoparticles (MNPs) as the reaction platform, and a portable blood glucose meter (PGM) as the detection method. Gold nanoparticles (AuNPs) were labeled with glucose oxidase (GOx) and alkyne-functionalized, terminally thiolated ssDNA (C2). In the presence of Cu2+ and ascorbate, the functionalized AuNPs were captured onto MNPs modified with azide-functionalized ssDNA (C1) via the Cu+-catalyzed alkyne-azide cycloaddition reaction. The GOx on the AuNPs' surface oxidized glucose (Glu) into gluconic acid and H2O2, reducing the Glu content in the reaction solution, which was quantitatively detected by the PGM. Under optimal conditions, the PGM response of the system showed a good linear relationship with the logarithm of Cu2+ concentration in the range of 0.05 to 10.00 μmol/L, with a detection limit of 0.03 μmol/L (3σ). In actual tap water samples, the spiked recovery rate of Cu2+ was between 92.30% and 113.33%, and the relative standard deviation was between 0.14% and 0.34%, meeting the detection requirements for Cu2+ in real water samples.

Rapid detection of SARS-CoV-2 spike protein using a magnetic-assisted electrochemical biosensor based on functionalized CoFe2O4 magnetic nanomaterials

The outbreak of novel coronavirus pneumonia (COVID-19) in 2019 has garnered widespread attention. The virus exhibits high contagiousness, and in certain cases, it can lead to recurrent infections. Therefore, it is imperative to develop portable, sensitive, and accurate sensors to promptly detect infected individuals, control the virus's transmission, and determine suitable treatment strategies. In this study, we proposed a magnetically-assisted method employing CFO@CS-Au MNP as the substrate material, which was functionalized with human angiotensin-converting enzyme (ACE2) for efficient capture of SARS-CoV-2 spike protein in solution. Subsequently, the captured protein was sensitively detected through differential pulse voltammetry (DPV) electrical analysis. The linear detection range of the labeled GCE/MNP/GA/ACE2/BSA electrochemical sensor is from 1 pg/mL to 10 μg/mL, with a minimum detection limit of 0.15 pg/mL. Furthermore, the fabricated GCE/MNP/GA/ACE2/BSA sensor achieved satisfactory recoveries of SARS-CoV-2 spike protein in saliva and nasal swab samples within 10 min. These results indicate that this magnetically-assisted biosensor has established a solid foundation for the swift on-site detection of COVID-19.

Overview on the Design of Magnetically Assisted Electrochemical Biosensors

Electrochemical biosensors generally require the immobilization of recognition elements or capture probes on the electrode surface. This may limit their practical applications due to the complex operation procedure and low repeatability and stability. Magnetically assisted biosensors show remarkable advantages in separation and pre-concentration of targets from complex biological samples. More importantly, magnetically assisted sensing systems show high throughput since the magnetic materials can be produced and preserved on a large scale. In this work, we summarized the design of electrochemical biosensors involving magnetic materials as the platforms for recognition reaction and target conversion. The recognition reactions usually include antigen-antibody, DNA hybridization, and aptamer-target interactions. By conjugating an electroactive probe to biomolecules attached to magnetic materials, the complexes can be accumulated near to an electrode surface with the aid of external magnet field, producing an easily measurable redox current. The redox current can be further enhanced by enzymes, nanomaterials, DNA assemblies, and thermal-cycle or isothermal amplification. In magnetically assisted assays, the magnetic substrates are removed by a magnet after the target conversion, and the signal can be monitored through stimuli-response release of signal reporters, enzymatic production of electroactive species, or target-induced generation of messenger DNA.

Signal-on photoelectrochemical immunoassay for salivary cortisol based on silver nanoclusters-triggered ion-exchange reaction with CdS quantum dots

Nowadays, the epidemic, employment, and academic pressures are seriously affecting our physical and mental health. Herein, we designed a magneto-controlled photoelectrochemical immunosensor for noninvasive monitoring of salivary cortisol regarded as a pressure biomarker. A competitive immunoassay model was established by coupling bovine serum albumin-cortisol modified magnetic beads (MB-BSA-cortisol) with silver nanoclusters (Ag NCs)-labelled anti-cortisol antibody, and quantity analysis was operated by photoelectrochemical measurement of the CdS/Au electrode as an ion-exchange platform. Accompanying the formation of immune complexes, the carried Ag NCs were readily dissolved with nitric acid to produce abundant silver ions, which transferred to the electrode for ion-exchange reaction with CdS quantum dots to produce Ag₂S, a new electron–hole capture site, leading to a decrease in the photocurrent intensity. The photocurrent signal gradually recovered with the increase of concentration of target cortisol, acquiring the signal-on mode competitive immunosensing system, which is propitious to the detection of small molecules. Within optimal conditions, this sensor had a satisfactory linear relationship in the range of 0.0001–100 ng mL⁻¹ with favorable repeatability, specificity, and acceptable method accuracy. The detection limit was as low as 0.06 pg mL⁻¹. In addition, this strategy provided new thought for the test of other small-molecule analytes and immunosensor applied in the complex biological system.

Nanoconfinement Effect for Signal Amplification in Electrochemical Analysis and Sensing

Owing to the urgent need for electrochemical analysis and sensing of trace target molecules in various fields such as medical diagnosis, agriculture and food safety, and environmental monitoring, signal amplification is key to promoting analysis and sensing performance. The nanoconfinement effect, derived from nanoconfined spaces and interfaces with sizes approaching those of target molecules, has witnessed rapid development for ultra-sensitive analyzing and sensing. In this review, the two main types of nanoconfinement systems - confined nanochannels and planes - are assessed and recent progress is highlighted. The merits of each nanoconfinement system, the nanoconfinement effect mechanisms, and applications for electrochemical analysis and sensing are summarized and discussed. This review aims to help deepen the understanding of nanoconfinement devices and their effects in order to develop new analysis and sensing applications for researchers in various fields.

Contribution of Nanomaterials to the Development of Electrochemical Aptasensors for the Detection of Antimicrobial Residues in Food Products

The detection of antimicrobial residues in food products of animal origin is of utmost importance. Indeed antimicrobial residues could be present in animal derived food products because of animal treatments for curative purposes or from illegal use. The usual screening methods to detect antimicrobial residues in food are microbiological, immunological or physico-chemical methods. The development of biosensors to propose sensitive, cheap and quick alternatives to classical methods is constantly increasing. Aptasensors are one of the major trends proposed in the literature, in parallel with the development of immunosensors based on antibodies. The characteristics of electrochemical sensors (i.e., low cost, miniaturization, and portable instrumentation) make them very good candidates to develop screening methods for antimicrobial residues in food products. This review will focus on the recent advances in the development of electrochemical aptasensors for the detection of antimicrobial residues in food products. The contribution of nanomaterials to improve the performance characteristics of electrochemical aptasensors (e.g., Sensitivity, easiness, stability) in the last ten years, as well as signal amplification techniques will be highlighted.

Aptamer-Based Biosensors for Environmental Monitoring

Due to their relative synthetic and chemical simplicity compared to antibodies, aptamers afford enhanced stability and functionality for the detection of environmental contaminants and for use in environmental monitoring. Furthermore, nucleic acid aptamers can be selected for toxic targets which may prove difficult for antibody development. Of particular relevance, aptamers have been selected and used to develop biosensors for environmental contaminants such as heavy metals, small-molecule agricultural toxins, and water-borne bacterial pathogens. This review will focus on recent aptamer-based developments for the detection of diverse environmental contaminants. Within this domain, aptamers have been combined with other technologies to develop biosensors with various signal outputs. The goal of much of this work is to develop cost-effective, user-friendly detection methods that can complement or replace traditional environmental monitoring strategies. This review will highlight recent examples in this area. Additionally, with innovative developments such as wearable devices, sentinel materials, and lab-on-a-chip designs, there exists significant potential for the development of multifunctional aptamer-based biosensors for environmental monitoring. Examples of these technologies will also be highlighted. Finally, a critical perspective on the field, and thoughts on future research directions will be offered.

Thiocholine-triggered reaction in personal glucose meters for portable quantitative detection of organophosphorus pesticide

A portable and user-friendly method using personal glucose meters for on-site quantitative detection of organophosphorus pesticide (OP) was developed. The inhibition of organophosphorus compounds on acetylcholinesterase (AChE) leads to reduced yields of thiocholine formed by the enzymatic hydrolysis of acetylthiocholine chloride. Ferricyanide ([Fe(CN)₆]^3-), the mediator used in glucose test strips for electron transfer to the electrode, can be rapidly reduced to ferrocyanide ([Fe(CN)₆]^4-) by thiocholine. This reaction enables direct measurement of thiocholine by personal glucose meters in the same way as measuring the glucose in blood, offering an interesting choice to quantify OP. After incubation of AChE for 30 min and enzymatic reaction of 10 min, the yield of thiocholine was measured by a personal glucose meter, achieving detection limit of 5 μg L^-1 for paraoxon. The proposed method was successfully applied to the detection in apples and cucumbers, presenting promising potential for on-site OP detection in food samples.

Immunomagnetic separation and size-based detection of Escherichia coli O157 at the meniscus of a membrane strip

We developed a facile method for the detection of pathogenic bacteria using gold-coated magnetic nanoparticle clusters (Au@MNCs) and porous nitrocellulose strips. Au@MNCs were synthesized and functionalized with half-fragments of Escherichia coli O157 antibodies. After the nanoparticles were used to capture E. coli O157 in milk and dispersed in a buffer solution, one end of a test strip was dipped into the solution. Due to the size difference between the E. coli–Au@MNC complexes (approximately 1 μm) and free Au@MNCs (approximately 180 nm), only E. coli–Au@MNC complexes accumulated at the meniscus of the test strip and induced a color change. The color intensity of the meniscus was proportional to the E. coli concentration, and the detection limit for E. coli in milk was 10³ CFU mL⁻¹ by the naked eye. The presence of E. coli–Au@MNC complexes at the meniscus was confirmed using a real-time PCR assay. The developed method was highly selective for E. coli when compared with Salmonella typhimurium, Listeria monocytogenes, and Staphylococcus aureus.

E. coli–Au/MNC complexes accumulate at the meniscus of the test strip where the flow velocity reaches a maximum.