Recent advances in electrochemical aptasensors and genosensors for the detection of pathogens

In recent years, pathogenic microorganisms have caused significant mortality rates and antibiotic resistance and triggered exorbitant healthcare costs. These pathogens often have high transmission rates within human populations. Rapid diagnosis is crucial in controlling and reducing the spread of pathogenic infections. The diagnostic methods currently used against individuals infected with these pathogens include relying on outward symptoms, immunological-based and, some biomolecular ones, which mainly have limitations such as diagnostic errors, time-consuming processes, and high-cost platforms. Electrochemical aptasensors and genosensors have emerged as promising diagnostic tools for rapid, accurate, and cost-effective pathogen detection. These bio-electrochemical platforms have been optimized for diagnostic purposes by incorporating advanced materials (mainly nanomaterials), biomolecular technologies, and innovative designs. This review classifies electrochemical aptasensors and genosensors developed between 2021 and 2023 based on their use of different nanomaterials, such as gold-based, carbon-based, and others that employed other innovative assemblies without the use of nanomaterials. Inspecting the diagnostic features of various sensing platforms against pathogenic analytes can identify research gaps and open new avenues for exploration.

An electrochemical assay for sensitive detection of Acinetobacter baumannii gene

A new genosensor, which allows sensitive and selective detection of Acinetobacter baumannii gene sequence was developed herein. In this assay, capture probe of Acinetobacter baumannii was immobilized on the surface of chitosan modified single-use pencil graphite electrodes (c-PGEs) to obtain Acinetobacter baumannii genosensor. Then, Acinetobacter baumannii target DNA sequence was recognized after solid-state hybridization on c-PGE genosensor by measuring guanine signal via differential pulse voltammetry (DPV). In order to improve hybridization efficiency, experimental parameters affecting all assay steps are studied and the analytical performance of the genosensor was tested. The low limit of detection (LOD) for Acinetobacter baumannii target DNA sequence was obtained as 1.86 nM with developed genosensor. The selectivity of the proposed assay was then tested in the presence of 1-base mismatch, or two different type of non-complementary sequences and no interference effect was observed. The proposed electrochemical assay protocol is easy, convenient, and rapid which can be a decent alternative to existing methods.

Electrochemical measuring of reactive oxygen species levels in the blood to detect ratio of high-density neutrophils, suitable to alarm presence of cancer in suspicious cases

Here for the first time, a real-time electrochemical assay on unprocessed blood was designed to detect the presence of cancer in patients. The system has been based on the recently approved pathway, which indicates that the abundance of immature and mature low-density neutrophils (LDNs) with reduced ROS production in peripheral blood is increased with the presence of active cancer tumors. Reduced ROS/H₂O₂ released from LDNs play the main role in determining the ROS/H₂O₂ levels of peripheral blood. In contrast, HDNs with increased levels of released ROS/H₂O₂ have higher concentrations than LDNs in normal cases. Hence, the reduced level of ROS species in peripheral blood recorded by our carbon nanostructure decorated sensor in less than 30 seconds showed a great pre-warning about the presence of non-treated cancer in patients with suspicious mass who have been sent for further evaluations.

A label-free electrochemical assay for coronavirus IBV H120 strain quantification based on equivalent substitution effect and AuNPs-assisted signal amplification

A label-free electrochemical strategy is proposed combining equivalent substitution effect with AuNPs-assisted signal amplification. According to the differences of S1 protein in various infectious bronchitis virus (IBV) strains, a target DNA sequence that can specifically recognize H120 RNA forming a DNA-RNA hybridized double-strand structure has been designed. Then, the residual single-stranded target DNA is hydrolyzed by S1 nuclease. Therefore, the content of target DNA becomes equal to the content of virus RNA. After equivalent coronavirus, the target DNA is separated from DNA-RNA hybridized double strand by heating, which can partly hybridize with probe 2 modified on the electrode surface and probe 1 on AuNPs’ surface. Thus, AuNPs are pulled to the surface of the electrode and the abundant DNA on AuNPs’ surface could adsorb a large amount of hexaammineruthenium (III) chloride (RuHex) molecules, which produce a remarkably amplified electrochemical response. The voltammetric signal of RuHex with a peak near − 0.28 V vs. Ag/AgCl is used as the signal output. The proposed method shows a detection range of 1.56e⁻⁹ to 1.56e⁻⁶ μM with the detection limit of 2.96e⁻¹⁰ μM for IBV H120 strain selective quantification detection, exhibiting good accuracy, stability, and simplicity, which shows a great potential for IBV detection in vaccine research and avian infectious bronchitis diagnosis.

Efficient immobilization of aptamers on the layered double hydroxide nanohybrids for the electrochemical proteins detection

Despite the use of layered double hydroxides (LDH) in different electrochemical (bio)sensors, the construction of aptasensors using LDH-based surfaces was not reported to the best of our knowledge. This may be due to the lack of a suitable linker to attach aptamers to the LDH-modified surface. LDH-based aptasensors are established here as very sensitive and reliable devices in serum and cerebrospinal fluid (CSF) analysis. 5'-NH₂ DNA aptamer probes were immobilized on the LDH-based surfaces in a vertical conformation without any linker materials. Due to the low electron conductivity of the LDH, carbon nanotubes (CNT) with high electronic conductivity and high surface area were combined with LDH. Thrombin was used as a model protein for aptasensing. The sensor shows a linear range of 0.005-12,000 pmol L^-1 and a limit of detection of 0.1 fmol L^-1. Moreover, the aptasensor was used for the sensing of thrombin in CSF and serum samples acquired from both healthy and patients with different disease.

In situ formed zinc oxide/graphitic carbon nitride nanohybrid for the electrochemical determination of 4-nitrophenol

The electrochemical determination of 4-nitrophenol using a nanohybrid consisting of glassy carbon (GC) and zinc oxide/graphitic carbon nitride (ZnO/g-CN nanosheet), is described. The ZnO/g-CN nanohybrid was in situ synthesized by chemical method and well characterized using absorption spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopic analysis. It was observed that the nanosized ZnO particles were present inside the sheet-like g-CN nanostructure. The nanohybrid-modified electrode showed an enhanced electrocatalytic response for 4-nitrophenol reduction compared with the bare GC electrode. The assay exhibited linear ranges of 13.4-100 μM and 100-1000 μM for 4-NP determination. The limit of detection and limit of quantification were 4.0 and 13.4 μM, respectively, at the working potential of - 0.85 V. An appreciable precision was found towards the stability of the assay in the determination. It provides selectivity against inorganic and organic substances such as calcium chloride, potassium chloride, nitrobenzene, uric acid, 1-chloro,2,4-dinitrobenzene, 1-bromo,2-nitrobenzene and 1-iodo,2-nitrobenzene. The practical applicability of the assay was also checked in the analysis of real water samples and satisfactory recovery of 4-NP was found. Schematic representation of the synthesis of zinc oxide (ZnO) nanostructures incorporated graphitic carbon nitride nanosheets (g-C₃N₄ NSs) and its application in the voltammetric determination of 4-nitrophenol (4-NP) is presented. The nanohybrid assay showed selectivity among coexisting compounds and good recovery in real sample analysis.

Electrochemical detection of Toxocara canis excretory-secretory antigens in children from rural communities in Esmeraldas Province, Ecuador: association between active infection and high eosinophilia

Background

The diagnosis of active Toxocara canis infections in humans is challenging. Larval stages of T. canis do not replicate in human tissues and disease may result from infection with a single T. canis larva. Recently, we developed a nanobody-based electrochemical magnetosensor assay with superior sensitivity to detect T. canis excretory-secretory (TES) antigens. Here, we evaluate the performance of the assay in children from an Ecuadorian birth cohort that followed children to five years of age.

Methods

Samples were selected based on the presence of peripheral blood eosinophilia and relative eosinophil counts. The samples were analyzed by the nanobody-based electrochemical magnetosensor assay, which utilizes a bivalent biotinylated nanobody as capturing agent on the surface of streptavidin pre-coated paramagnetic beads. Detection was performed by a different nanobody chemically labelled with horseradish peroxidase.

Results

Of 87 samples tested, 33 (38%) scored positive for TES antigen recognition by the electrochemical magnetosensor assay. The average concentration of TES antigen in serum was 2.1 ng/ml (SD = 1.1). The positive result in the electrochemical assay was associated with eosinophilia > 19% (P = 0.001). Parasitological data were available for 57 samples. There was no significant association between positivity by the electrochemical assay and the presence of other soil-transmitted helminth infections.

Conclusions

Our nanobody-based electrochemical assay provides highly sensitive quantification of TES antigens in serum and has potential as a valuable tool for the diagnosis of active human toxocariasis.

Graphene/aptamer probes for small molecule detection: from in vitro test to in situ imaging

Small molecules are key targets in molecular biology, environmental issues, medicine and food industry. However, small molecules are challenging to be detected due to the difficulty of their recognition, especially in complex samples, such as in situ in cells or animals. The emergence of graphene/aptamer probes offers an excellent opportunity for small molecule quantification owing to their appealing attributes such as high selectivity, sensitivity, and low cost, as well as the potential for probing small molecules in living cells or animals. This paper (with 130 refs.) will review the application of graphene/aptamer probes for small molecule detection. We present the recent progress in the design and development of graphene/aptamer probes enabling highly specific, sensitive and rapid detection of small molecules. Emphasis is placed on the success in their development and application for monitoring small molecules in living cells and in vivo systems. By discussing the key advances in this field, we wish to inspire more research work of the development of graphene/aptamer probes for both on-site or in situ detection of small molecules and its applications for investigating the functions of small molecules in cells in a dynamic way. Graphical abstract Graphene/aptamer probes can be used to construct different platforms for detecting small molecules with high specificity and sensitivity, both in vitro and in situ in living cells and animals.

Natural receptor-based competitive immunoelectrochemical assay for ultra-sensitive detection of Siglec 15

Sialic acid-binding immunoglobulin-like lectin 15 (Siglec 15) is a novel immunomodulatory target and was identified as an immune suppressor in the tumor microenvironment. Accurate assessment of Siglec 15 expression levels is critical for cancer prognosis and treatment. In this work, a natural receptor-based immunoelectrochemical sensor is designed to mimic the interaction between Siglec 15 and DNA_X-activation protein (DAP 12) in the cellular signal pathway. DAP 12 labeled with the electrochemical signal molecule Fc is recognized by Siglec 15 through specific interaction on the electrode surface and used as the signal reporter. Anti-Siglec 15 modified MNPs (MNPs-Ab) were used as the extraction agent for the magnetic extraction of target analytes in complex matrices. Free Anti-Siglec 15 will "squeeze out" the DAP 12-Fc to bind the Siglec 15 on the electrode surface, resulting a sensitive electrochemical signal change according to the Siglec 15 concentration in sample. Natural receptor-based competitive assay ensure the efficient binding between antibody and Siglec 15 and decrease the nonspecific interaction. Therefore, this simple natural receptor-based competitive assay with sensitivity and selectivity has potential for practical clinical application.

A sandwich-type electrochemical aptasensor for Mycobacterium tuberculosis MPT64 antigen detection using C60NPs decorated N-CNTs/GO nanocomposite coupled with conductive PEI-functionalized metal-organic framework

The present work described a novel sandwich-type electrochemical aptasensor for rapid and sensitive determination of Mycobacterium tuberculosis MPT64 antigen. Herein, a novel carbon nanocomposite composed of fullerene nanoparticles, nitrogen-doped carbon nanotubes and graphene oxide (C₆₀NPs-N-CNTs/GO) was facilely synthesized for the first time, which not only possessed a large specific surface area and excellent conductivity, but also exhibited outstanding inherent electroactive property, and therefore served as nanocarrier and redox nanoprobe simultaneously. Gold nanoparticles (AuNPs) was then uniformly anchored onto the surface of such nanocomposite via Au-N bonds to bind with MPT64 antigen aptamer Ⅱ (MAA Ⅱ), forming the tracer label to realize generation and amplification of electrochemical signal. Additionally, conductive polyethyleneimine (PEI)-functionalized Fe-based metal-organic framework (P-MOF) was used as a sensing platform to absorb bimetallic core-shell Au-Pt nanoparticles (Au@Pt), which could accelerate electron transfer and increase the immobilization of MPT64 antigen aptamer Ⅰ (MAA Ⅰ). After the typical sandwich-type protein-aptamer recognition, the inherent electroactivity of the tracer label was provoked by tetraoctylammonium bromide (TOAB), leading to a well-defined current response. Under the optimum condition, the proposed aptasensor showed a wide linear range for MPT64 detection from 1 fg/mL to 1 ng/mL with a limit of detection (LOD) as low as 0.33 fg/mL. More importantly, it was successfully used for MPT64 antigen detection in human serum, exhibiting a promising prospect for TB diagnosis in clinical practice.

Electrochemical analysis of 8-hydroxy-2'-deoxyguanosine with enhanced sensitivity based on exonuclease-mediated functional nucleic acid

In this work, an electrochemical method for sensitive analysis of 8-hydroxy-2'-deoxyguanosine, a key biomarker that is widely used to study oxidative injury-related diseases, is proposed based on exonuclease-mediated functional nucleic acid. In the design, exonuclease can not only distinguish the existence of target, but also suppress the background noise, thus the sensitivity can be enhanced. Moreover, DNAzyme designed in the functional nucleic acid can further improve the sensitivity of the analysis during signal generation process. Therefore, exonuclease-mediated functional nucleic acid may ensure high sensitivity of the assay. Further studies reveal that the detection of 8-hydroxy-2'-deoxyguanosine can be achieved with a linearity from 0.01 nM to 7.0 μM and a detection limit of 6.82 pM. The new method has also been successfully applied to the determination of 8-OHdG in urine with good results, indicating its great potential for practical use.

A quantitative electrochemical assay for liver injury

Liver diseases represent a vastly underestimated and historically neglected public health problem, disproportionately affecting those in low- and middle- income countries (LMICs). Patients on hepatotoxic medications, such as HIV and TB medications, need consistent monitoring of liver function as part of their standard of care. In high resource settings, this is often the case, but in LMICs traditional methods fail due to high cost and lack of proper equipment, supplies and trained personnel. To address this gap in technology and patient care, we have developed a quantitative, electrochemical assay capable of quantifying levels of alanine aminotransferase (ALT), a primary biomarker associated with liver function. We can quantify ALT with increased sensitivity (1.53 nA/(U/L*mm²) and over a wide, linear concentration range (40-1990 U/L). The assay demonstrated in this study can be used to overcome several pressing challenges associated with effective, timely treatment of liver disease in LMICs.

A DNA functionalized porphyrinic metal-organic framework as a peroxidase mimicking catalyst for amperometric determination of the activity of T4 polynucleotide kinase

An electrochemical method is described for the sensitive detection of the activity of the enzyme T4 polynucleotide kinase (PNK) by using a DNA functionalized porphyrinic metal-organic framework (L/(Fe-P)n-MOF). In the presence of PNK, the hairpin oligonucleotide (HP1) becomes phosphorylated, and the trigger is released by lambda exonuclease (λ exo). The trigger DNA hybridizes with hairpin probe (immobilized on the gold electrode) to form a nicking endonuclease cleavage site. Thus, a single-strand capture probe is employed to hybridize with L/(Fe-P)n-MOF. The (Fe-P)n-MOF is a peroxidase mimicking material with high catalytic efficiency. By using this amplification strategy, an electrochemical signal is procured that allows for the determination of T4 PNK in the 1.0 mU·mL^-1 to 1.0 U·mL^-1 with a detection limit of 0.62 mU·mL^-1. The method is selective and can be used to screen for enzyme inhibitors. Conceivably, the (Fe-P)n-MOF can also be used to detect other analytes via its peroxidase-mimicking activity. Graphical abstract Schematic presentation of T4 polynucleotide kinase (PNK) detection. Two hairpin DNAs (HP) and a porphyrinic metal-organic framework with peroxidase-mimicking activity are used. The detection limit is 0.62 mU mL^-1 with enzyme assisted signal amplification. This method is selective and can be used to screen for enzyme inhibitors.

Aptamer-based determination of tumor necrosis factor α using a screen-printed graphite electrode modified with gold hexacyanoferrate

An aptamer based method is presented for the voltammetric determination of human tumor necrosis factor alpha (TNF-α). Layers of gold hexacyanoferrate (AuHCF) and gold nanoparticles (AuNPs) were directly immobilized on a graphite screen-printed electrode (SPE). Through the strong interaction between cyanide ions (CN^-) of AuHCF and AuNPs, gold nanoparticles are assembled on the modified SPE, and this allows for the covalent immobilization of thiolated aptamers against TNF-α (TNF-α-Apt). On incubation of the aptasensor with of TNF-α, the Apt/TNF-α complex is formed, and this leads to a hindered electron transfer and to a decrease in the peak current of the redox probe. Under optimum conditions and at a typical working as low as 0.1 V (vs. a silver pseudo electrode), the electrode works in the 10 pg.mL^-1 to 40 μg.mL^-1 TNF-α concentration range, with a 5.5 pg.mL^-1 detection limit. The high sensitivity and wide detection range of this method allowed TNF-α to in human serum be detected even at very low concentrations. Graphical abstract Schematic diagram for fabrication of aptasensor: (a,b) formation of AuHCF film by electrodeposition;

A new electrochemical immunosensor for sensitive detection of prion based on Prussian blue analogue

Based on Co-Co Prussian blue analogue (Co-Co PBA), a novel immunosensor has been developed for sensitive detection of prion protein (PrP^C). Gold nanoparticles (AuNPs)-modified Co-Co PBA nanocubes (PBA-AuNPs) worked as a support of the antibody (Ab2) of PrP^C to obtain Ab2-PBA-AuNPs composite and also as the signal source for PrP^C assay. When PrP^C existed, Ab2-PBA-AuNPs could be introduced to the surface of another antibody of PrP^C (Ab1) modified AuNPs/GC electrode (the gold nanoparticles-modified glassy carbon electrode) through specific antigen-antibody interaction between PrP^C and its antibodies to form the Ab1-PrP^C-Ab2 sandwich structure. With the help of KOH aqueous solution, PBA generated a large DPV response. The response peak currents were linear with the logarithmic values of the concentration of PrP^C in the range from 0.075pgmL^-1 to 100pgmL^-1 with the detection limit of 0.014pgmL^-1. Also, the immunosensor showed good selectivity and reproducibility. Based on the simple sensing structure and good analytical performance, the developed immunosensor may have promising applications in practical assay of infectious isoform of prion (PrP^Sc) and other proteins by simply changing the related antibody.

Ratiometric electrochemical assay for sensitive detecting microRNA based on dual-amplification mechanism of duplex-specific nuclease and hybridization chain reaction

We propose a ratiometric electrochemical assay for detecting microRNA (miRNA) on the basis of dual-amplification mechanism by using distinguishable electrochemical signals from thionine (Thi) and ferrocene (Fc). The thiol-modified and ferrocene-labeled hairpin capture probes (CP) are first immobilized on an Au electrode via Au-S reaction. The target miRNA hybridizes with CP and unfolding the hairpin structure of CP to form miRNA-DNA duplexes. Then, kamchatka crab duplex specific nuclease (DSN) specifically cleaves the DNA in miRNA-DNA duplexes, leading to the release of miRNA and another cleaves cycle, meanwhile, numerous Fc leaves away from the electrode surface and leads to the signal-off of Fc. The residual fragment on electrode surface acts as a HCR primer to form dsDNA polymers through in situ HCR with the presence of the primer and two probes (HDNA and HDNA'), resulting in the capture of numerous DNA/Au NPs/Thi and the signal-on of Thi. The dual-amplification mechanism significantly amplifies the decrease of Fc signal and the increase of Thi signal for ratiometric readout (I_Thi/I_Fc), thus providing a sensitive method for the selective detection of miR-141 with a detection limit down to 11aM. The dual-signal ratiometric outputs have an intrinsic self-calibration to the effects from system, which is promising to be applied in biosensing and clinical diagnosis.

High-performance and versatile electrochemical aptasensor based on self-supported nanoporous gold microelectrode and enzyme-induced signal amplification

Herein, novel and versatile electrochemical aptasensors were constructed on a self-supported nanoporous gold (np-Au) microelectrode, integrating with an exonuclease III (Exo III) induced signal amplification strategy. Self-supported np-Au microelectrode with 3D bicontinuous nanoporous structures possesses tremendously large specific area, clean surface, high stability and biocompatibility, bringing about significant advantages in both molecular recognition and signal response. As paradigms, two analytes of bisphenol A (BPA) and ochratoxin A (OTA) were selected to demonstrate the superiority and versatility of designed aptasensors. Trace amounts of mDNA (associated with BPA or OTA concentration) hybridized with cDNA strands assembled on np-Au microelectrode, activating the cleavage reaction with Exo III. Thus, cDNA was digested and mDNA was released to undergo a new hybridization and cleavage cycle. Finally, residual cDNA strands were recognized by methylene blue labelled rDNA/AuNPs with the assistance of hDNA to generate the electrochemical signals, which were used to quantitatively monitor targets. Under the optimized conditions, prepared aptasensors exhibited wide linear ranges (25pg/mL to 2ng/mL for BPA, 10pg/mL to 5ng/mL for OTA) with ultralow detection limits (10pg/mL for BPA, 5pg/mL for OTA), excellent selectivity and stability, and reliable detection in real samples. This work opens a new horizon for constructing promising electrochemical aptasensors for environmental monitoring, medical diagnostics and food safety.

A novel and simple cell-based electrochemical biosensor for evaluating the antioxidant capacity of Lactobacillus plantarum strains isolated from Chinese dry-cured ham

The analysis of antioxidants in foodstuffs has become an active area of research, leading to the recent development of numerous methods for assessing antioxidant capacity. Here we described the fabrication and validation of a novel and simple cell-based electrochemical biosensor for this purpose. The biosensor is used to assess the antioxidant capacity of cell-free extracts from Lactobacillus plantarum strains isolated from Chinese dry-cured ham. The biosensor relies on the determination of cellular reactive oxygen species (ROS) (the flux of H₂O₂ released from RAW 264.7 macrophage cells) to indirectly assess changes in intracellular oxidative stress level as influenced by L. plantarum strains. A one-step acidified manganese dioxide (a-MnO₂) modified gold electrode (GE) was used to immobilize RAW 264.7 macrophage cells, which were then encapsulated in a 3D cell culture system consisting of alginate/ graphene oxide (NaAlg/GO). The biosensor exhibited a rapid and sensitive response for the detection of H₂O₂ released from RAW264.7 cells. The detection limit was 0.02μM with a linear response from 0.05μM to 0.85μM and the biosensor was shown to have good stability and outstanding repeatability. This technique was then used for evaluating the antioxidant ability of extracts from L. plantarum NJAU-01. According to the electrochemical investigations and assays of SEM, TEM, and ROS, these cell-free extracts effectively reduced the oxidative stress levels in RAW264.7 cells under external stimulation. Extracts from L. plantarum strains at a dose of 10¹⁰CFU/mL showed the highest antioxidant activities with a relative antioxidant capacity (RAC) rate of 88.94%. Hence, this work provides a simple and efficient electrochemical biosensing platform based on RAW264.7 cells for fast, sensitive and quantitative assessment of antioxidant capacity of L. plantarum strains. The method demonstrates its potential for rapid screening for evaluating antioxidant properties of samples.

Monitoring of microbial cell viability using nanostructured electrodes modified with Graphene/Alumina nanocomposite

Microbial infections are rapidly increasing; however most of the existing microbiological and molecular detection methods are time consuming and/or cannot differentiate between the viable and dead cells which may overestimate the risk of infections. Therefore, a bioelectrochemical sensing platform with a high potential to the microbial-electrode interactions was designed based on decorated graphene oxide (GO) sheet with alumina (Al₂O₃) nanocrystals. GO-Al₂O₃ nanocomposite was synthesized using self-assembly of GO and Al₂O₃ and characterized using the scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), Raman-spectroscopy, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Enhancement of electrocatalytic activity of the composite-modified electrode was demonstrated. Thus, using the GO-Al₂O₃ nanocomposite modified electrode, the cell viability was determined by monitoring the bioelectrochemical response of the living microbial cells (bacteria and yeast) upon stimulation with carbon source. The bioelectrochemical assay was optimized to obtain high sensitivity and the method was applied to monitor cell viability and screen susceptibility of metabolically active cells (E. coli, B. subtilis, Enterococcus, P. aeruginosa and Salmonella typhi) to antibiotics such as ampicillin and kanamycin. Therefore, the developed assay is suitable for cell proliferation and cytotoxicity testing.

Aptasensors for quantitative detection of kanamycin

Up till now, various techniques have been developed to detect kanamycin in biological samples. However, due to some problems involved in these methods including time-consuming, expensive equipment and high consumption of reagents, new strategies for detection and quantitative determination of kanamycin are needed. Aptamer-based biosensors with unique recognition capability have attracted more attention of scientists because of its rapid response, high sensitivity and simple fabrication. Hence, we summarized optical and electrochemical kanamycin aptasensors and focuses on recent advances and modern techniques in aptasensor-based kanamycin detection techniques in order to provide readers with an inclusive understanding of its improvement and progress.

Sensitive and low-background electrochemical assay of corin activity via supramolecular recognition and rolling circle amplification

Corin is an important member of type II transmembrane serine proteases that is involved in a variety of cardiovascular and pregnancy-related diseases. Herein, a sensitive and low-background electrochemical method is proposed to assay the activity of corin. In principle, a peptide comprising both the substrate motif of corin and binding site of cucurbit[8]uril (CB[8]) is first designed and immobilized on the electrode surface. Thereafter, via CB[8]-mediated supramolecular recognition, a DNA-primer is recruited, subsequently triggering the rolling circle amplification (RCA) reaction. In this way, a succeeding propagation of DNA strands is achieved on the electrode surface, which would produce remarkable repelling effect against the electrochemical species [Fe(CN)6](3-/4-), and thereby yield a highly minimized background signal. However, in the presence of activated corin, the peptide is specifically recognized and cleaved, breaching the recruitment of DNA primer as well as the RCA reaction, which decreases the repulsion to [Fe(CN)6](3-/4-), leading to a remarkable electrochemical response. As a result, the proposed assay method can sensitively determine the activity of corin with a detection limit of 0.92 pM, and can further be directly used in maternal plasma samples. Therefore, this method may provide a promising tool for pathological research and clinical diagnosis of corin-related diseases.

Real-time electrocatalytic sensing of cellular respiration

In the present work we develop a real-time electrochemical mediator assay to enable the assessment of cell numbers and chemical toxicity. This allowed us to monitor metabolism down to a single cell in a low cost easy to use rapid assay which is not possible with current technology. The developed assay was based on the determination of oxygen. This was made possible via the use of electrochemical mediator ferrocene carboxylic acid (FcA). The FcA showed distinctive catalytic properties in interacting with reactive oxygen species generated from oxygen when compared to ferrocene methanol (FcMeOH). A deeper insight into the chemistry controlling this behaviour is provided. The behaviour is then taken advantage of to develop a cellular aerobic respiration assay. We describe the properties of the FcA system to detect, in real-time, the oxygen consumption of Escherichia coli DH5-α (E. coli). We demonstrated that the FcA-based oxygen assay is highly sensitive, and using a population of cells, oxygen consumption rates could be calculated down to a single cell level. More importantly, the results can be accomplished in minutes, considerably outperforming current commercially available biooxygen demand assays. The developed assay is expected to have a significant impact in diverse fields and industries, ranging from environmental toxicology through to pharmaceutical and agrochemical industries.