Disposable electrochemical aptasensor array by using in situ DNA hybridization inducing silver nanoparticles aggregate for signal amplification

Electrochemical detection of poly(ADP-ribose) polymerase-1 with silver nanoparticles as signal labels by integrating the advantages of homogeneous reaction with surface-tethered detection

Poly(ADP-ribose)polymerase-1 (PARP1) could be activated by binding to nucleic acids with specific sequences, thus catalyzing the poly-ADP-ribosylation (PARylation) of target proteins including PARP1 itself. Most of the previously reported electrochemical methods for the determination of PARP1 were relied on the electrostatic interactions, which required the pre-immobilization of DNA on an electrode for the capture of PARP1. Herein, we reported an "immobilization-free" electrochemical strategy for the assays of PARP1 on the basic of avidin-biotin interaction. Once PARP1 was activated by binding with the specific double-stranded DNA (dsDNA) in a homogeneous solution, the biotinylated nicotinamide adenine dinucleotide (biotin-NAD+) was transferred onto PARP1, resulting in the formation of biotinylated PAR polymers. The resulting biotinylated PAR polymers were then captured by a neutravidin (NA)-modified electrode through avidin-biotin interactions. The rich biotin moieties in the PAR polymers allowed for the capture of NA-modified silver nanoparticles (NA-AgNPs) through the avidin-biotin interactions. The surface-tethered AgNPs produced a well-defined electrochemical signal due to the characteristic solid-state Ag/AgCl process. The "immobilization-free", electrostatic interaction-independent electrochemical biosensor exhibited low background current, high sensitivity, and good stability. It has achieved the determination of PARP1 with a detection limit down to 0.7 mU. The biosensor was further applied to determine the inhibition efficiency of potential inhibitors with a satisfactory result. This method shows promising potential applications in PARP1-related clinical diagnosis and drug discovery.

Advances in the application of logic gates in nanozymes

Nanozymes are a class of nanomaterials with biocatalytic function and enzyme-like activity, whose advantages include high stability, low cost, and mass production. They can catalyze the substrates of natural enzymes based on specific nanostructures and serve as substitutes for natural enzymes. Their applied research involves a wide range of fields such as biomedicine, environmental governance, agriculture, and food. Molecular logic gates are a new cross-disciplinary discipline, which can simulate the function of silicon circuits on a molecular scale, perform single or multiple input logic operations, and generate logic outputs. A molecular logic gate is a binary operation that converts an input signal into an output signal according to the rules of Boolean logic, generating two signals, a high level, and a low level. The high and low levels represent the "true" and "false" values of the logic gates, and their outputs correspond to "l" and "0" of the molecular logic gates, respectively. The combination of nanozymes and logic gates is a novel and attractive research direction, and the cross-application of the two brings new opportunities and ideas for various fields, such as the construction of efficient biocomputers, intelligent drug delivery systems, and the precise diagnosis of diseases. This review describes the application of logic gates based on nanozymes, which is expected to provide a certain theoretical foundation for researchers' subsequent studies.

2D MOF-enhanced SPR sensing platform: Facile and ultrasensitive detection of Sulfamethazine via supramolecular probe

Sulfamethazine (SMZ) is widely present in the environment and can cause severe allergic reactions and cancer in humans. Accurate and facile monitoring of SMZ is crucial for maintaining environmental safety, ecological balance, and human health. In this work, a real-time and label-free surface plasmon resonance (SPR) sensor was devised using a two-dimensional metal-organic framework with superior photoelectric performance as an SPR sensitizer. The supramolecular probe was incorporated at the sensing interface, allowing for the specific capture of SMZ from other analogous antibiotics through host-guest recognition. The intrinsic mechanism of the specific interaction of the supramolecular probe-SMZ was elucidated through the SPR selectivity test in combination with analysis by density functional theory, including p-π conjugation, size effect, electrostatic interaction, π-π stacking, and hydrophobic interaction. This method facilitates a facile and ultrasensitive detection of SMZ with a limit of detection of 75.54 pM. The accurate detection of SMZ in six environmental samples demonstrates the potential practical application of the sensor. Leveraging the specific recognition of supramolecular probes, this direct and simple approach offers a novel pathway for the development of novel SPR biosensors with outstanding sensitivity.

Nanostructured N, S, and P-Doped Elaeagnus Angustifolia Gum-Derived Porous Carbon with Electrodeposited Silver for Enhanced Electrochemical Sensing of Acetaminophen

Acetaminophen (N-acetyl-p-aminophenol, APAP) is regularly used for antipyretic and analgesic purposes. Overdose or long-term exposure to APAP could lead to liver damage and hepatotoxicity. In this study, the approach of enhanced electrochemical detection of APAP by nanostructured biomass carbon/silver was developed. Porous biomass carbon derived from Elaeagnus Angustifolia gum was prepared by pyrolysis with co-doping of electron-rich elements of nitrogen, sulfur, and phosphorus. The electrodeposition of silver onto a glassy carbon electrode modified with porous carbon could enhance the sensing signal towards APAP. Two linear ranges from 61 nM to 500 μM were achieved with a limit of detection of 33 nM. The developed GCE sensor has good anti-interference, stability, reproducibility, and human urine sample analysis performance. The silver-enhanced biomass carbon GCE sensor extends the application of biomass carbon, and its facile preparation approach could be used in constructing disposable sensing chips in the future.

Signaling strategies of silver nanoparticles in optical and electrochemical biosensors: considering their potential for the point-of-care

Silver nanoparticles (AgNPs) have long been overshadowed by gold NPs' success in sensor and point-of-care (POC) applications. However, their unique physical, (electro)chemical, and optical properties make them excellently suited for such use, as long as their inherent higher instability toward oxidation is controlled. Recent advances in this field provide novel strategies that demonstrate that the AgNPs' inherent capabilities improve sensor performance and enable the specific detection of analytes at low concentrations. We provide an overview of these advances by focusing on the nanosized Ag (in the range of 1-100 nm) properties with emphasis on optical and electrochemical biosensors. Furthermore, we critically assess their potential for point-of-care sensors discussing advantages as well as limitations for each detection technique. We can conclude that, indeed, strategies using AgNP are ready for sensitive POC applications; however, research focusing on the simplification of assay procedures is direly needed for AgNPs to make the successful jump into actual applications.

Biosensing chips for cancer diagnosis and treatment: a new wave towards clinical innovation

Recent technological advances in nanoscience and material designing have led to the development of point-of-care devices for biomolecule sensing and cancer diagnosis. In situ and portable sensing devices for bedside, diagnosis can effectively improve the patient’s clinical outcomes and reduce the mortality rate. Detection of exosomal RNAs by immuno-biochip with increased sensitivity and specificity to diagnose cancer has raised the understanding of the tumor microenvironment and many other technology-based biosensing devices hold great promise for clinical innovations to conquer the unbeatable fort of cancer metastasis. Electrochemical biosensors are the most sensitive category of biomolecule detection sensors with significantly low concentrations down to the atomic level. In this sense, this review addresses the recent advances in cancer detection and diagnosis by developing significant biological sensing devices that are believed to have better sensing potential than existing facilities.

Coupled Multiphysics Modelling of Sensors for Chemical, Biomedical, and Environmental Applications with Focus on Smart Materials and Low-Dimensional Nanostructures

Low-dimensional nanostructures have many advantages when used in sensors compared to the traditional bulk materials, in particular in their sensitivity and specificity. In such nanostructures, the motion of carriers can be confined from one, two, or all three spatial dimensions, leading to their unique properties. New advancements in nanosensors, based on low-dimensional nanostructures, permit their functioning at scales comparable with biological processes and natural systems, allowing their efficient functionalization with chemical and biological molecules. In this article, we provide details of such sensors, focusing on their several important classes, as well as the issues of their designs based on mathematical and computational models covering a range of scales. Such multiscale models require state-of-the-art techniques for their solutions, and we provide an overview of the associated numerical methodologies and approaches in this context. We emphasize the importance of accounting for coupling between different physical fields such as thermal, electromechanical, and magnetic, as well as of additional nonlinear and nonlocal effects which can be salient features of new applications and sensor designs. Our special attention is given to nanowires and nanotubes which are well suited for nanosensor designs and applications, being able to carry a double functionality, as transducers and the media to transmit the signal. One of the key properties of these nanostructures is an enhancement in sensitivity resulting from their high surface-to-volume ratio, which leads to their geometry-dependant properties. This dependency requires careful consideration at the modelling stage, and we provide further details on this issue. Another important class of sensors analyzed here is pertinent to sensor and actuator technologies based on smart materials. The modelling of such materials in their dynamics-enabled applications represents a significant challenge as we have to deal with strongly nonlinear coupled problems, accounting for dynamic interactions between different physical fields and microstructure evolution. Among other classes, important in novel sensor applications, we have given our special attention to heterostructures and nucleic acid based nanostructures. In terms of the application areas, we have focused on chemical and biomedical fields, as well as on green energy and environmentally-friendly technologies where the efficient designs and opportune deployments of sensors are both urgent and compelling.

Electroconductive Polyaniline–Ag-ZnO Green Nanocomposite Material

Metal-conducting polyaniline (PANI)-based nanocomposite materials have attracted attention in various applications due to their synergism of electrical, mechanical, and optical properties of the initial components. Herein, metal-PANI nanocomposites, including silver nanoparticle-polyaniline (AgNP-PANI), zinc oxide nanoparticle-polyaniline (ZnONP-PANI), and silver-zinc oxide nanoparticle-polyaniline (Ag–ZnONP-PANI), were prepared using the two processes. Nanocomposite-based electrode platforms were prepared by depositing AgNPs, ZnONPs, or Ag–ZnONPs on a PANI modified glass carbon electrode (GCE) in the presence of 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide/N-Hydroxysuccinimide (EDC/NHS, 1:2) as coupling agents. The incorporation of AgNPs, ZnONPs, and Ag–ZnONPs onto PANI was confirmed by UV-Vis spectrophotometry, which showed five absorbance bands at 216 nm, 412 nm, 464 nm, 550 nm, and 831 nm (i.e., transition of π-π*, π-polaron band transition, polaron-π* electronic transition, and AgNPs). The FTIR characteristic signatures of the nanocomposite materials exhibited stretching arising from C–H aromatic, C–O, and C–N stretching mode for benzenoid rings, and =C–H plane bending vibration formed during protonation. The CV voltammograms of the nanocomposite materials showed a quasi-reversible behavior with increased redox current response. Notably, AgNP–PANI–GCE electrode showed the highest conductivity, which was attributed the high conductivity of silver. The increase in peak currents exhibited by the composites shows that AgNPs and ZnONPs improve the electrical properties of PANI, and they could be potential candidates for electrochemical applications.

DNA-templated electrodeposition of silver nanoparticles for direct and label-free aptasensing of ochratoxin A

We present in this work, an aptasensing strategy based on the DNA-templated electrodeposition of silver nanoparticles (AgNPs). The homogeneous electro-deposition of AgNPs on screen printed carbon electrode (SPCE) surface was achieved based on a unique aptamer scaffold. This was constructed by immobilizing a DNA aptamer on SPCE by electrochemical oxidation of its amine groups. The electrodeposition of AgNPs was investigated before and after the addition of the aptamer's specific target; the mycotoxin, ochratoxin A (OTA). Electrochemical characterization by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed the effect of the scaffold layer on the electrodeposition of AgNPs. The conformational change induced by aptamer after binding its targeted molecule affects AgNPs electrodeposition and the electron transfer thus allowing OTA detection by cyclic voltammetry. The voltammograms showed a good proportionality between the analyte concentration and the current response. The constructed platform allowed the quantitative aptasensing of OTA within the range of (1.56-400 ng/mL) and the detection limit of 0.6 ng/mL. In term of aptasensor applicability, the proposed strategy showed excellent performance in rice samples.

In Situ Assembly of Nanomaterials and Molecules for the Signal Enhancement of Electrochemical Biosensors

The physiochemical properties of nanomaterials have a close relationship with their status in solution. As a result of its better simplicity than that of pre-assembled aggregates, the in situ assembly of nanomaterials has been integrated into the design of electrochemical biosensors for the signal output and amplification. In this review, we highlight the significant progress in the in situ assembly of nanomaterials as the nanolabels for enhancing the performances of electrochemical biosensors. The works are discussed based on the difference in the interactions for the assembly of nanomaterials, including DNA hybridization, metal ion-ligand coordination, metal-thiol and boronate ester interactions, aptamer-target binding, electrostatic attraction, and streptavidin (SA)-biotin conjugate. We further expand the range of the assembly units from nanomaterials to small organic molecules and biomolecules, which endow the signal-amplified strategies with more potential applications.

3D printed enzymatic microchip for multiplexed electrochemical biosensing

The low-cost e-fabrication of specialized multianalyte biosensors within the point-of-care (POC) settings in a few minutes remains a great challenge. Unlike prefabricated biosensors, 3D printing seems to be able to meet this challenge, empowering the end user with the freedom to create on-demand devices adapted to immediate bioanalytical need. Here, we describe a novel miniature all-3D-printed 4-electrode biochip, capable of the simultaneous determination of different biomarkers in a single assay. The chip is utterly fabricated via an one-step 3D printing process and it is connected to a mini portable bi-potentiostant, permitting simultaneous measurements. The bioanalytical capability of the microchip is demonstrated through the simultaneous amperometric determination of two cardiac biomarkers (cholesterol and choline) in the same blood droplet, via enzymatic assays developed on its two tiny integrated electrodes. The simultaneous determination of cholesterol and choline is free from cross-talk phenomena and interferences offering limits of detection much lower than the cut-off levels of these biomarkers in blood for coronary syndromes. The biodevice is an easy-constructed, low-cost, sensitive and e-transferable POC chip with wide scope of applicability to other enzymatic bioassays.

Aptamer-based sensing of breast cancer biomarkers: a comprehensive review of analytical figures of merit

INTRODUCTION

Accurate determination of the aberrantly expressed biomarkers such as human epidermal growth factor receptor 2 (HER2), carcinoembryonic antigen (CEA), platelet-derived growth factor (PDGF), mucin 1 (MUC1), and vascular endothelial growth factor VEGF₁₆₅ have played an essential role in the clinical management of the breast cancer. Assessment of these cancer-specific biomarkers has conventionally relied on time-taking methods like the enzyme-linked immunosorbent assay and immunohistochemistry. However, recent development in the aptamer-based diagnostics has allowed developing tools that may substitute the conventional means of biomarker assessment in breast cancer. Adopting the aptamer-based diagnostic tools (aptasensors) to clinical practices will depend on their analytical performance on clinical samples.

AREAS COVERED

In this review, we provide an overview of the analytical merits of HER2, CEA, PDGF, MUC1, and VEGF₁₆₅ aptasensors. Scopus and Pubmed databases were searched for studies reporting aptasensor development for the listed breast cancer biomarkers in the past one decade. Linearity, detection limit, and response time are emphasized.

EXPERT OPINION

In our opinion, aptasensors have proven to be on a par with the antibody-based methods for detection of various breast cancer biomarkers. Though robust validation of the aptasensors on significant sample size is required, their ability to detect pathophysiological range of biomarkers suggest the possibility of future clinical adoption.

Signal amplification by electro-oligomerisation for improved isoproturon detection

A novel concept is introduced for signal amplification in electrochemical sensing: the electro-oligomerisation stripping voltammetry, which has been applied here to the improved detection of the isoproturon herbicide in spring waters as a proof-of-principle. It involves a potentiostatic accumulation step onto a glassy carbon electrode (at +1.5 V vs Ag/AgCl reference electrode for 300 s) leading to the formation of an oligomeric film, which is then detected by cathodic stripping square wave voltammetry (SWV). The presence and composition of the film are confirmed by confocal Raman spectroscopy. Its characterisation by cyclic voltammetry demonstrates the reversible nature of the electrodeposited material, confirming its interest for sensitive detection by SWV. Adding a mesoporous silica membrane with vertically oriented nanochannels further enhances the sensitivity of the sensor, exhibiting a linear response in the 10-100 μM concentration range. This effect was even more interesting for real media analysis thanks to the permselective properties of such nanoporous coating in rejecting interferences and/or surface fouling agents. The method should be applicable to other analytes that are usually not detectable by conventional accumulation/stripping voltammetry.

3D matrixed DNA self-nanocatalyzer as electrochemical sensitizers for ultrasensitive investigation of DNA 5-methylcytosine

DNA methylation plays an important role in a variety of human diseases. Thus, accurately analyze 5-methylcytosine in different DNA segments is of great significance. Herein, we proposed a novel 3D matrixed DNA self-nanocatalyzer via gold nanoparticles (AuNPs) supporting DNA self-hybridization with hemin as biomimetic enzyme and methylene blue (MB) as electrochemical mediator, which was employed as an efficient electrochemical sensitizer for the ultrasensitive bioassay of DNA 5-methylcytosine. Meanwhile, the AuNPs, graphitic carbon nitride (g-C₃N₄) and reduced graphene oxide (rGO) was prepared as AuNPs/g-C₃N₄@rGO nanocomposites to coat on the electrode surface to immobilize the capture hairpin DNA (CH). In the presence of target DNA with 5-methylcytosine, the target DNA could hybridize with CH via the hyperstable triple-helix formation. Based on the specific biorecognition between biotin and streptavidin and immune recognition between anti-5-methylcytosine antibodies and 5-methylcytosine sites on the target DNA, the 3D matrixed DNA self-nanocatalyzer could be captured onto the electrode surface to generate an amplified electrochemical signal related to the concentration of 5-methylcytosine. Under the optimal conditions, the proposed strategy performed a linear range from 10^-17 M to 10^-8 M with a detection limit of 8.6 aM. Remarkably, this strategy could be expanded easily to various biomarkers, including protein, DNA, phosphorylation and glycosylation, providing a promising strategy for clinical diagnosis and mechanism investigation of various diseases.

Modification-free amperometric biosensor for the detection of wild-type p53 protein based on the in situ formation of silver nanoparticle networks for signal amplification

Sensitive and accurate quantification of wild-type p53 protein is of great importance for biological research and clinical diagnosis. Herein, a modification-free amperometric biosensor was proposed for sensitive detection of wild-type p53 protein by the signal amplification of silver nanoparticles (AgNPs) networks formed in situ on electrode surface. Double-stranded DNA (dsDNA) probe containing two consensus sites was immobilized on gold electrode surface to capture wild-type p53 protein. The cysteine thiol and amine groups on the exterior of the protein allowed for the attachment of bare AgNPs through the AgS or AgN interactions. Meanwhile, benzene-1,4-dithiol (BDT) molecules in solution triggered the assembly of more AgNPs on electrode surface through the AgS interactions, thus leading to the in situ formation of AgNPs networks for signal amplification. The target at the concentration as low as 0.1 pM can be readily determined. This method was further applied to determine wild-type p53 protein in spiked human serum and cell lysates with satisfactory results. Moreover, the biosensor is regenerative and does not require the modification of AgNPs with recognition element for signal readout. The modification-free strategy can potentially be applied to develop novel biosensors for detection of other biological macromolecules.

α-Synuclein Oligomer Detection with Aptamer Switch on Reduced Graphene Oxide Electrode

Protein aggregation of alpha-synuclein (α-Syn) is implicated in Parkinson's disease (PD), and, thus, α-Syn aggregates are a potentially promising candidate biomarker for PD diagnosis. Here, we describe a simple and sensitive electrochemical sensor to monitor the aggregation of α-Syn for early PD diagnosis. The sensor utilizes methylene blue (MB)-tagged aptamer (Apt) adsorbed on electrochemically reduced graphene oxide (ERGO) by π-π stacking. The binding of α-Syn oligomer to the Apt induces desorption of the Apt from the ERGO surface, which leads to the electrochemical signal change. The resulting sensor allowed the highly sensitive and selective detection of α-Syn oligomer according to the voltammetric change. Under optimized conditions, the linear range of detection was observed to be from 1 fM to 1 nM of the α-Syn oligomer and the limit of detection (LOD) was estimated to be 0.64 fM based on S/N = 3. The sensor also showed good reproducibility and stability, enabling real sample analysis of the α-Syn oligomer in human blood serum. With its ultrasensitivity and good performance for α-Syn oligomer detection, the sensor provides one promising tool for the early diagnosis of PD.

A high-energy sandwich-type self-powered biosensor based on DNA bioconjugates and a nitrogen doped ultra-thin carbon shell

A high-energy self-powered sensing platform for the ultrasensitive detection of proteins is developed based on enzymatic biofuel cells (EBFCs) by using DNA bioconjugate assisted signal amplification.

A review on recent developments in optical and electrochemical aptamer-based assays for mycotoxins using advanced nanomaterials

This review (with 163 refs) covers the recent developments of nanomaterial-based optical and electrochemical sensors for mycotoxins. The review starts with a brief discussion on occurrence, distribution, toxicity of mycotoxins and the legislations in monitoring their levels. It further outlines the research methods, various recognition matrices and the strategies involved in the development of highly sensitive and selective sensor systems. It also points out the salient features and importance of aptasensors in the detection of mycotoxins along with the different immobilization methods of aptamers. The review meticulously discusses the performance of different optical and electrochemical sensors fabricated using aptamers coupled with nanomaterials (CNT, graphene, metal nanoparticles and metal oxide nanoparticles). The review addresses the limitations in the current developments as well as the future challenges involved in the successful construction of aptasensors with the functionalized nanomaterials. Graphical abstract Recent developments in nanomaterial based aptasensors for mycotoxins are summarized. Specifically, the efficiency of the nanomaterial coupled aptasensors (such as CNT, graphene, metal nanoparticles and metal oxide nanoparticles) in optical and electrochemical methods are discussed.

Fiber optic surface plasmon resonance biosensor for detection of PDGF-BB in serum based on self-assembled aptamer and antifouling peptide monolayer

Herein, a home-build fiber optic surface plasmon resonance (FO-SPR) biosensing platform has been developed for highly sensitive detection of platelet-derived growth factor (PDGF-BB) based aptamer-functionalized AuNPs for signal enhancement. In this biosensor, the PDGF-BB aptamer was used to specifically capture PDGF-BB, and the antifouling peptide demonstrated great ability for resisting non-specific adsorption. After a sandwich reaction, the aptamer, PDGF-BB and aptamer-functionalized AuNPs complexes were formed on the fiber optic (FO) probe surface to significantly amplify FO-SPR signal. This method exhibited a broad detection range from 1 to 1000 pM of PDGF-BB and a low detection limit of 0.35 pM. Moreover, this biosensor was successfully applied to the detection of PDGF-BB in 10% human serum samples without suffering from serious interference owing to the excellent antifouling property of the peptide. Thus, this developed FO-SPR biosensor could be a potential alternative device for proteins determination, even as a point-of-care diagnostic tool (POCT) in clinical application.

Electrochemical Detection and Characterization of Nanoparticles with Printed Devices

Innovative methods to achieve the user-friendly, quick, and highly sensitive detection of nanomaterials are urgently needed. Nanomaterials have increased importance in commercial products, and there are concerns about the potential risk that they entail for the environment. In addition, detection of nanomaterials can be a highly valuable tool in many applications, such as biosensing. Electrochemical methods using disposable, low-cost, printed electrodes provide excellent analytical performance for the detection of a wide set of nanomaterials. In this review, the foundations and latest advances of several electrochemical strategies for the detection of nanoparticles using cost-effective printed devices are introduced. These strategies will equip the experimentalist with an extensive toolbox for the detection of nanoparticles of different chemical nature and possible applications ranging from quality control to environmental analysis and biosensing.

Sensitive and rapid detection of pathogenic bacteria from urine samples using multiplex recombinase polymerase amplification

Bacterial infections may cause severe diseases such as tuberculosis, sepsis, nephritis and cystitis. The rapid and sensitive detection of bacteria is a prerequisite for the treatment of these diseases. The current gold standard for bacterial identification is bacteriological culture. However, culture-based identification takes 3-7 days, which is time-consuming and laborious. In this study, bacteria in urine samples were enriched using a portable filter-based pipette. Then, a centrifugal chip was constructed to detect multiple pathogenic bacteria from urine samples by integrating the DNA extraction, multiplex recombinase polymerase amplification (RPA) and fluorescent detection together. This eliminated the time-consuming cultivation step, and thus accelerated the diagnosis of the urinary tract infections (UTIs). The five major pathogenic bacteria in UTIs were detected in this study, which are Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa, Staphylococcus aureus and Salmonella typhimurium. Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa and Staphylococcus aureus were successfully detected with limits of detection of 100 CFU mL-1 from urine samples within 40 min. Salmonella typhimurium was successfully detected with a limit of detection of 1000 CFU mL-1 from urine samples. The chip-based bacteria detection proposed in this study is a promising tool for sensitive, accurate, and multiplex identification of bacteria in clinical urine samples of UTIs and bacteriuria.

Ultrasensitive enzyme-free fluorescent detection of VEGF165 based on target-triggered hybridization chain reaction amplification

Sensitive detection of vascular endothelial growth factor (VEGF165) is important for early cancer disease diagnosis in the clinic. A sensitive fluorescent sensing platform for VEGF165 detection is developed in this work. It is based on a target-triggered hybridization chain reaction (HCR) and graphene oxide (GO) selective fluorescence quenching. In this assay, in the presence of the VEGF165, the hairpin structure of Hp opens up and the initiation sequence will be exposed to Hp1 to open its hairpin structure. Then the opened Hp1 hybridizes with Hp2 to expose the complementary sequence of Hp1 which hybridizes with Hp1 again by HCR. Thus HCR would be initiated, generating super-long dsDNA. After the HCR, the double strands of the HCR product cannot be adsorbed on the GO surface. As a result, the HCR product gives a strong fluorescence signal which is dependent on the concentration of VEGF165. By using VEGF165 as a model analyte, the assay provides a highly sensitive fluorescence detection method for VEGF165 with a detection limit down to 20 pg mL-1. The proposed aptasensing strategy based on target-triggered HCR amplification can thus be realized. It was successfully applied to the determination of VEGF165 in spiked human serum, urine and saliva. Therefore, it can easily have wide applications in the diagnosis of vital diseases.

Target-programmed and autonomous proximity binding aptasensor for amplified electronic detection of thrombin

The development of sensitive and simple approaches capable of monitoring trace amounts of protein biomarkers is appealing for disease diagnosis and treatment. Towards this end, we have developed an electrochemical sensing platform for sensitive and simple detection of protein biomarkers by using thrombin as the model target molecules via a target-programmed proximity binding amplification approach. The binding of thrombin to the aptamer sequences in the partial dsDNA duplex probes induces the release of the ssDNA trigger strands, which catalyze subsequent assembly formation of many methylene blue (MB)-tagged proximate DNA motifs with the presence of the DNA fuel strands through cascaded toehold-mediated strand displacement reactions. Due to the proximity-binding effect, these MB-tagged proximate DNA motifs anneal with the capture probes on the sensor surface with significantly enhanced stability against the corresponding single component counterpart, thereby pulling the MB tags close to the sensor surface and generating substantially amplified signal responses for sensitive determination of thrombin down to 23.6 pM. In addition, such aptasensor can specifically discriminate thrombin from other interference proteins, and can also be utilized to monitor thrombin in diluted serum samples, demonstrating its great potential for sensitive determination of proteins for early disease diagnosis.

Recent advances on aptamer-based biosensors to detection of platelet-derived growth factor

Platelet-derived growth factor (PDGF-BB), a significant serum cytokine, is an important protein biomarker in diagnosis and recognition of cancer, which straightly rolled in proceeding of various cell transformations, including tumor growth and its development. Fibrosis, atherosclerosis are certain appalling diseases, which PDGF-BB is near to them. Generally, the expression amount of PDGF-BB increases in human life-threatening tumors serving as an indicator for tumor angiogenesis. Thus, identification and quantification of PDGF-BB in biomedical fields are particularly important. Affinity chromatography, immunohistochemical methods and enzyme-linked immunosorbent assay (ELISA), conventional methods for PDGF-BB detection, requiring high-cost and complicated instrumentation, take too much time and offer deficient sensitivity and selectivity, which restrict their usage in real applications. Hence, it is essential to design and build enhanced systems and platforms for the recognition and quantification of protein biomarkers. In the past few years, biosensors especially aptasensors have been received noticeable attention for the detection of PDGF-BB owing to their high sensitivity, selectivity, accuracy, fast response, and low cost. Since the role and importance of developing aptasensors in cancer diagnosis is undeniable. In this review, optical and electrochemical aptasensors, which have been applied by many researchers for PDGF-BB cancer biomarker detection, have been mentioned and merits and demerits of them have been explained and compared. Efforts related to design and development of aptamer-based biosensors using nanoparticles for sensitive and selective detection of PDGF-BB have been reviewed considering: Aptamer importance as recognition elements, principal, application and the recent improvements and developments of aptamer based optical and electrochemical methods. In addition, commercial biosensors and future perspectives for rapid and on-site detection of PDGF-BB have been summarized.

A biolayer interferometry-based enzyme-linked aptamer sorbent assay for real-time and highly sensitive detection of PDGF-BB

Accurate, fast and sensitive detection of disease-specific protein biomarkers, especially in blood, urine, or other bodily fluids, is an important approach to achieve early disease diagnosis. Platelet-derived growth factor-BB (PDGF-BB), a widely used biomarker, is involved in a substantial number of serious diseases, such as hepatic fibrosis, atherosclerosis, age-related macular degeneration and diabetic eye disease and is often over-expressed in human malignant tumors. Therefore, the development of sensitive and specific detection methods for PDGF-BB is of great importance for the early diagnosis of disease and assessments of patient recovery. In the current study, a biolayer interferometry-based enzyme-linked aptamer sorbent assay (BLI-ELASA) was successfully established for rapid (20-25min), high-throughput (8 or 16 samples) and real-time monitoring of PDGF-BB in clinical samples. The method exhibited a broad detection range from 0.5 to 1000ng/mL of PDGF-BB (good linear range from 0.5 to 10ng/mL), with a low detection limit of 0.08ng/mL. Moreover, BLI-ELASA was applied to the detection of PDGF-BB in spiked serum and urine samples and showed a high degree of selectivity for PDGF-BB, good reproducibility, and stability. We believe that the methodology in this work can be easily adapted to detect other biomolecules in clinical samples, including viruses, pathogens and toxins, in a rapid, sensitive, high-throughput and real-time manner.

Highly efficient electrochemical sensing platform for sensitive detection DNA methylation, and methyltransferase activity based on Ag NPs decorated carbon nanocubes

In this paper, we reported a sensitive and selective electrochemical method for quantify DNA methylation, analyzing DNA MTase activity and screening of MTase inhibitor based on silver nanoparticles (Ag NPs) decorated carbon nanocubes (CNCs) as signal tag. The Ag NPs/CNCs was prepared by in situ growth of nanosilver on carboxylated CNCs and used as a tracing tag to label antibody. The sensor was prepared by immobilizing the double DNA helix structure on the surface of gold electrode. When DNA MTase was introduced, the probe was methylated. Successively, anti-5-methylcytosine antibody labeled Ag NPs/CNCs was specifically conjugated on the CpG methylation site. The electrochemical stripping signal of the Ag NPs was used to monitor the activity of MTase. The electrochemical signal has a linear relationship with M.SssI activities ranging from 0.05 to 120U/mL with a detection limit of 0.03U/mL. In addition, we also demonstrated the method could be used for rapid evaluation and screening of the inhibitors of MTase. The newly designed strategy avoid the requirement of deoxygenation for electrochemical assay, and thus provide a promising potential in clinical application.

Shell-encoded Au nanoparticles with tunable electroactivity for specific dual disease biomarkers detection

The exploration of electroactive labelling with tailorable and strong differential pulse voltammetry (DPV) responses is of great importance in accurate and sensitive screening of a panel of biomarkers related to cancer. Herein, shell-encoded gold nanoparticles (Au NPs) are fabricated and give rise to shell species-dominated DPV peak potentials. Two independent DPV peaks appear at -0.08V for Au@Cu₂O core-shell NPs and 0.26V for Au@Ag core-shell NPs. Shell-encoded Au NPs drastically exhibit shell thickness-tunable amplified peak currents. The non-interfering and amplified DPV responses enable shell-encoded Au NPs to be an alternative electrochemical signal amplifier for dual screening of carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP). The limits of detection (LODs) are calculated to be 1.8pg/mL for CEA and 0.3pg/mL for AFP. In comparison to the parallel single-analyte assays, shell-encoded Au NPs engineered electrochemical aptasensors offer multiplexing capability and show significant prospects in biomedical research and early diagnosis of diseases.

Aptamer/Protein Proximity Binding-Triggered Molecular Machine for Amplified Electrochemical Sensing of Thrombin

The development of convenient and sensitive methods without involving any enzymes or complex nanomaterials for the monitoring of proteins is of great significance in disease diagnostics. In this work, we describe the validation of a new aptamer/protein proximity binding-triggered molecular machinery amplification strategy for sensitive electrochemical assay of thrombin in complex serum samples. The sensing interface is prepared by self-assembly of three-stranded DNA complexes on the gold electrode. The association of two distinct functional aptamers with different sites of thrombin triggers proximity binding-induced displacement of one of the short single-stranded DNAs (ssDNAs) from the surface-immobilized three-stranded DNA complexes, exposing a prelocked toehold domain to hybridize with a methylene blue (MB)-tagged fuel ssDNA strand (MB-DNA). Subsequent toehold-mediated strand displacement by the MB-DNA leads to the release and recycling of the aptamer/protein complexes and the function of the molecular machine. Eventually, a large number of MB-DNA strands are captured by the sensor surface, generating drastically amplified electrochemical responses from the MB tags for sensitive detection of thrombin. Our signal amplified sensor is completely enzyme-free and shows a dynamic range from 5 pM to 1 nM with a detection limit of 1.7 pM. Such sensor also has a high specificity for thrombin assay in serum samples. By changing the affinity probe pairs, the developed sensor can be readily expanded as a more general platform for sensitive detection of different types of proteins.

Thrombin aptasensor enabled by Pt nanoparticles-functionalized Co-based metal organic frameworks assisted electrochemical signal amplification

In this work, a Pt nanoparticles-functionalized Co-based metal organic frameworks (PtNPs@Co(II)MOFs@PtNPs) was synthesized and applied in electrochemical aptasensor for thrombin (TB) detection. First, the Co(II)MOFs@PtNPs were prepared via the mixed solvothermal method, which consists of inner Pt nanoparticles (PtNPs) encapsulated by aminofunctionalized Co(II)MOFs materials. Following that, additional PtNPs were adsorbed on the surface of Co(II)MOFs@PtNPs, resulting in the formation of PtNPs@Co(II)MOFs@PtNPs nanocomposite. The PtNPs@Co(II)MOFs@PtNPs nanocomposites with a large surface area were implimented as nanocarriers to immobilize a mass of TBA II for the formation of the TBA II bioconjugates that could be captured onto the electrode surface by sandwich-type format. Moreover, the PtNPs@Co(II)MOFs@PtNPs nanocomposites could directly use as redox tags for charge-generating and electron-transporting with the electron transfer from Co(II) to Co(III). Furthermore, in the presence of H₂O₂, the PtNPs@Co(II)MOF@PtNPs could effectively catalyze H₂O₂ oxidation with improvement electron transfer of redox probe, resulting in electrochemical signal amplification. Based on the above superior advantages, TB was determined in the concentration range from 0.1pM to 50nM with a detection limit of 0.33fM. Furthermore, the excellent sensitivity and selectivity can be easily established for quantitative analysis of other analytes.

Graphene oxide directed in-situ deposition of electroactive silver nanoparticles and its electrochemical sensing application for DNA analysis

The development of high-performance biosensing platform is heavily dependent on the recognition property of the sensing layer and the output intensity of the signal probe. Herein, we present a simple and highly sensitive biosensing interface for DNA detection on the basis of graphene oxide nanosheets (GONs) directed in-situ deposition of silver nanoparticles (AgNPs). The fabrication process and electrochemical properties of the biosensing interface were probed by electrochemical techniques and scanning electron microscopy. The results indicate that GONs can specifically adsorb at the single-stranded DNA probe surface, and induces the deposition of highly electroactive AgNPs. Upon hybridization with complementary oligonucleotides to generate the duplex DNA on the electrode surface, the GONs with the deposited AgNPs will be liberated from the sensing interface due to the inferior affinity of GONs and duplex DNA, resulting in the reduction of the electrochemical signal. Such a strategy combines the superior recognition of GONs toward single-stranded DNA and double-stranded DNA, and the strong electrochemical response of in-situ deposited AgNPs. Under optimal conditions, the biosensor can detect target DNA over a wide range from 10 fM to 10 nM with a detection limit of 7.6 fM. Also, the developed biosensor shows outstanding discriminating ability toward oligonucleotides with different mismatching degrees.

Design of dual working electrodes for concentration process in metalloimmunoassay

Electrochemical immunosensing, particularly through a metalloimmunoassay, is a promising approach for development of point-of-care (POC) diagnostics devices. This study investigated the structure of dual working electrodes (W1 and W2), used in a silver nanoparticles-labeled sandwich-type immunoassay and silver concentration process, paying special attention to the position of W1 relative to W2. The new structures of the dual working electrodes were fabricated for efficient silver concentration and evaluated experimentally, which showed that the duration of prereduction before current measurement decreased from 480 s to 300 s by transforming the position of W1 from 1 line to 2 lines or 6 parts. The experimental results were also compared with numerical simulations based on three-dimensional diffusion, and the prereduction step almost followed the three-dimensional diffusion equation. Using numerical simulations, the ideal structures of dual working electrodes were designed based on relationships between the structures and duration of prereduction or the LOD. In the case of 36 lines at an area ratio of W1 to W1 + W2 of 1 to 10, the prereduction duration decreased to 96 s. The dual working electrodes designed in this study promise to shorten the total analysis time and lower the LOD for POC diagnostics.