Sensitive immunosensor for tumor necrosis factor α based on dual signal amplification of ferrocene modified self-assembled peptide nanowire and glucose oxidase functionalized gold nanorod

Electrochemical protein biosensors for disease marker detection: progress and opportunities

The development of artificial intelligence-enabled medical health care has created both opportunities and challenges for next-generation biosensor technology. Proteins are extensively used as biological macromolecular markers in disease diagnosis and the analysis of therapeutic effects. Electrochemical protein biosensors have achieved desirable specificity by using the specific antibody-antigen binding principle in immunology. However, the active centers of protein biomarkers are surrounded by a peptide matrix, which hinders charge transfer and results in insufficient sensor sensitivity. Therefore, electrode-modified materials and transducer devices have been designed to increase the sensitivity and improve the practical application prospects of electrochemical protein sensors. In this review, we summarize recent reports of electrochemical biosensors for protein biomarker detection. We highlight the latest research on electrochemical protein biosensors for the detection of cancer, viral infectious diseases, inflammation, and other diseases. The corresponding sensitive materials, transducer structures, and detection principles associated with such biosensors are also addressed generally. Finally, we present an outlook on the use of electrochemical protein biosensors for disease marker detection for the next few years.

Aggregation-induced signal amplification strategy based on peptide self-assembly for ultrasensitive electrochemical detection of melanoma biomarker

The detection of melanoma circulating biomarker in liquid biopsies is current under evaluation for being potentially utilized for earlier cancer diagnosis and its metastasis. Herein, we developed a non-invasive electrochemical approach for ultrasensitive detection of the S100B, serving as a potential promising blood circulating biomarker of melanoma, based on an aggregation-induced signal amplification (AISA) strategy via in-situ peptide self-assembly. The fundamental principle of this assay is that the designed amphiphilic peptides (C16-Pep-Fc), fulfilling multiple functions, feature both a recognition region for specific binding to S100B and an aggregation (self-assembly) region for the formation of peptide nanomicelles under mild conditions. The C16 tails were encapsulated within the hydrophobic core of the aggregates, while the relatively hydrophilic recognition fragment Pep and Fc tag were exposed on the outer surface for subsequent recognition of S100B and signal output. AISA provided remarkable accumulation of electroactive Fc moieties that enabled ultrasensitive S100B detection of as low as 0.02 nM, which was 10-fold lower than un-amplified approach and better than previously reported assays. As a proof-of-concept study, further experiments also highlighted the good reproducibility and stability of AISA and demonstrated its usability when applied to simulated serum samples. Hence, this work not only presented a valuable assay tool for ultrasensitive detecting protein biomarker, but also advocated for the utilization of aggregation-induced signal amplification in electrochemical biosensing system, given its considerable potential for future practical applications.

Advancements in Biosensors Based on the Assembles of Small Organic Molecules and Peptides

Over the past few decades, molecular self-assembly has witnessed tremendous progress in a variety of biosensing and biomedical applications. In particular, self-assembled nanostructures of small organic molecules and peptides with intriguing characteristics (e.g., structure tailoring, facile processability, and excellent biocompatibility) have shown outstanding potential in the development of various biosensors. In this review, we introduced the unique properties of self-assembled nanostructures with small organic molecules and peptides for biosensing applications. We first discussed the applications of such nanostructures in electrochemical biosensors as electrode supports for enzymes and cells and as signal labels with a large number of electroactive units for signal amplification. Secondly, the utilization of fluorescent nanomaterials by self-assembled dyes or peptides was introduced. Thereinto, typical examples based on target-responsive aggregation-induced emission and decomposition-induced fluorescent enhancement were discussed. Finally, the applications of self-assembled nanomaterials in the colorimetric assays were summarized. We also briefly addressed the challenges and future prospects of biosensors based on self-assembled nanostructures.

Supramolecular peptide nano-assemblies for cancer diagnosis and therapy: from molecular design to material synthesis and function-specific applications

Peptide molecule has high bioactivity, good biocompatibility, and excellent biodegradability. In addition, it has adjustable amino acid structure and sequence, which can be flexible designed and tailored to form supramolecular nano-assemblies with specific biomimicking, recognition, and targeting properties via molecular self-assembly. These unique properties of peptide nano-assemblies made it possible for utilizing them for biomedical and tissue engineering applications. In this review, we summarize recent progress on the motif design, self-assembly synthesis, and functional tailoring of peptide nano-assemblies for both cancer diagnosis and therapy. For this aim, firstly we demonstrate the methodologies on the synthesis of various functional pure and hybrid peptide nano-assemblies, by which the structural and functional tailoring of peptide nano-assemblies are introduced and discussed in detail. Secondly, we present the applications of peptide nano-assemblies for cancer diagnosis applications, including optical and magnetic imaging as well as biosensing of cancer cells. Thirdly, the design of peptide nano-assemblies for enzyme-mediated killing, chemo-therapy, photothermal therapy, and multi-therapy of cancer cells are introduced. Finally, the challenges and perspectives in this promising topic are discussed. This work will be useful for readers to understand the methodologies on peptide design and functional tailoring for highly effective, specific, and targeted diagnosis and therapy of cancers, and at the same time it will promote the development of cancer diagnosis and therapy by linking those knowledges in biological science, nanotechnology, biomedicine, tissue engineering, and analytical science.

Electrochemical Biosensors for Cytokine Profiling: Recent Advancements and Possibilities in the Near Future

Cytokines are soluble proteins secreted by immune cells that act as molecular messengers relaying instructions and mediating various functions performed by the cellular counterparts of the immune system, by means of a synchronized cascade of signaling pathways. Aberrant expression of cytokines can be indicative of anomalous behavior of the immunoregulatory system, as seen in various illnesses and conditions, such as cancer, autoimmunity, neurodegeneration and other physiological disorders. Cancer and autoimmune diseases are particularly adept at developing mechanisms to escape and modulate the immune system checkpoints, reflected by an altered cytokine profile. Cytokine profiling can provide valuable information for diagnosing such diseases and monitoring their progression, as well as assessing the efficacy of immunotherapeutic regiments. Toward this goal, there has been immense interest in the development of ultrasensitive quantitative detection techniques for cytokines, which involves technologies from various scientific disciplines, such as immunology, electrochemistry, photometry, nanotechnology and electronics. This review focusses on one aspect of this collective effort: electrochemical biosensors. Among the various types of biosensors available, electrochemical biosensors are one of the most reliable, user-friendly, easy to manufacture, cost-effective and versatile technologies that can yield results within a short period of time, making it extremely promising for routine clinical testing.

Novel voltammetric tumor necrosis factor-alpha (TNF-α) immunosensor based on gold nanoparticles involved in thiol-functionalized multi-walled carbon nanotubes and bimetallic Ni/Cu-MOFs

TNF-α, as a pro-inflammatory cytokine, regulates some physiological and pathological courses. TNF-α level increases in some important diseases such as cancer, arthritis, and diabetes. In addition, it displays an important function in Alzheimer's and cardiovascular diseases. Herein, a novel, sensitive, and selective voltammetric TNF-α immunosensor was prepared by using gold nanoparticles involved in thiol-functionalized multi-walled carbon nanotubes (AuNPs/S-MWCNTs) as sensor platform and bimetallic Ni/Cu-MOFs as sensor amplification. Firstly, the sensor platform was developed on glassy carbon electrode (GCE) surface by using mixture of thiol-functionalized MWCNTs (S-MWCNTs) and AuNPs. Then, capture TNF-α antibodies were conjugated to sensor platform by amino-gold affinity. After capture TNF-α antibodies' immobilization, a new-type voltammetric TNF-α immunosensor was developed by immune reaction between AuNPs/S-MWCNTs immobilized with primer TNF-α antibodies and bimetallic Ni/Cu-MOFs conjugated with seconder TNF-α antibodies. The prepared TNF-α immunosensor was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), x-ray diffraction (XRD) method, x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), thermogravimetric analysis, Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). A linearity range of 0.01-1.0 pg mL^-1 and a low detection limit of 2.00 fg mL^-1 were also obtained for analytical applications.

Cerium oxide nanofiber based electroanalytical sensor for TNF-α detection: Improved interfacial stability with Nafion

The present work is aimed at improving the adhesion of nanomaterials at the interface of solid state working electrodes. Towards this, herein, an efficient method has been proposed that requires the electrode interface to be decorated with an optimally thin layer of Nafion. This selectively permeable layer ensures the stability of the sensor interface, without hampering the transport of biomolecules and electrons. As a case study, here, electrospun Cerium oxide nanofiber (CeNF) modified Glassy carbon electrodes (GCE) have been used as the sensing interface, and stability and performance of the GCE/CeNF/Nafion interface is evaluated using analytical electrochemistry. The CeNF is synthesized via electrospinning and is characterized using X-ray diffraction spectroscopy, Thermal gravimetry, Fourier transform infrared spectroscopy, and Field emission scanning electron microscopy. Further, detection of sepsis specific biomarker TNF-α from spiked buffer samples is demonstrated, as a case study, towards evaluating the effect of Nafion on the interfacial sensitivity. The achieved LOD of GCE/CeNF and GCE/CeNF/Nafion for TNF-α detection were 2.8 fg/mL and 1.2 fg/mL, respectively. A comparative analysis between the Electrochemical impedance spectroscopic (EIS) results of the GCE/CeNF and the GCE/CeNF/Nafion interfaces confirms the improvement in stability, without affecting the sensitivity and the limiting detection.

Electrochemical Applications of Ferrocene-Based Coordination Polymers

Ferrocene and its derivatives, especially ferrocene-based coordination polymers (Fc-CPs), offer the benefits of high thermal stability, two stable redox states, fast electron transfer, and excellent charge/discharge efficiency, thus holding great promise for electrochemical applications. Herein, we describe the synthesis and electrochemical applications of Fc-CPs and reveal how the incorporation of ferrocene units into coordination polymers containing other metals results in unprecedented properties. Moreover, we discuss the usage of Fc-CPs in supercapacitors, batteries, and sensors as well as further applications of these polymers, for example in electrocatalysts, water purification systems, adsorption/storage systems.

Electrochemical immunosensors for the detection of cytokine tumor necrosis factor alpha: A review

In this review, we focus on recent developments in nonlabeled@label-free and labeled@sandwich assay concepts of tumor necrosis factor-alpha (TNF-α) using numerous electrochemical approaches. The fundamental role of such nanostructured materials for the improvement of the analytical response and thus the analytical figures of merit of various TNF-α sensing operations were revealed. Also, this examination focused on recent developments in immuno-electrochemical cytokine TNF-α sensors based on nanostructured materials from 2006 to 2019.

Electrochemical Biosensors as Potential Diagnostic Devices for Autoimmune Diseases

An important class of biosensors is immunosensors, affinity biosensors that are based on the specific interaction between antibodies and antigens. They are classified in four classes based on the type of employed transducer: electrochemical, optical, microgravimetric, and thermometric and depending on the type of recognition elements, antibodies, aptamers, microRNAs and recently peptides are integrating parts. Those analytical devices are able to detect peptides, antibodies and proteins in various sample matrices, without many steps of sample pretreatment. Their high sensitivity, low cost and the easy integration in point of care devices assuring portability are attracting features that justify the increasing interest in their development. The use of nanomaterials, simultaneous multianalyte detection and integration on platforms to form point-of-care devices are promising tools that can be used in clinical analysis for early diagnosis and therapy monitoring in several pathologies. Taking into account the growing incidence of autoimmune disease and the importance of early diagnosis, electrochemical biosensors could represent a viable alternative to currently used diagnosis methods. Some relevant examples of electrochemical assays for autoimmune disease diagnosis developed in the last several years based on antigens, antibodies and peptides as receptors were gathered and will be discussed further.

Recent advances in designing nanomaterial based biointerfaces for electrochemical biosensing cardiovascular biomarkers

Early diagnosis of cardiovascular disease (CVD) is critically important for successful treatment and recovery of patients. At present, detection of CVD at early stages of its progression becomes a major issue for world health. The nanoscale electrochemical biosensors exhibit diverse outstanding properties, rendering them extremely suitable for the determination of CVD biomarkers at very low concentrations in biological fluids. The unique advantages offered by electrochemical biosensors in terms of sensitivity and stability imparted by nanostructuring the electrode surface together with high affinity and selectivity of bioreceptors have led to the development of new electrochemical biosensing strategies that have introduced as interesting alternatives to conventional methodologies for clinical diagnostics of CVD. This review provides an updated overview of selected examples during the period 2005-2018 involving electrochemical biosensing approaches and signal amplification strategies based on nanomaterials, which have been applied for determination of CVD biomarkers. The studied CVD biomarkers include AXL receptor tyrosine kinase, apolipoproteins, cholesterol, C-reactive protein (CRP), D-dimer, fibrinogen (Fib), glucose, insulin, interleukins, lipoproteins, myoglobin, N-terminal pro-B-type natriuretic peptide (BNP), tumor necrosis factor alpha (TNF-α) and troponins (Tns) on electrochemical transduction format. Identification of new specific CVD biomarkers, multiplex bioassay for the simultaneous determination of biomarkers, emergence of microfluidic biosensors, real-time analysis of biomarkers and point of care validation with high sensitivity and selectivity are the major challenges for future research.

Recent progress on the sensitive detection of cardiovascular disease markers by electrochemical-based biosensors

Cardiovascular disease is the most reason for deaths in all over the world. Hence, biomarkers of cardiovascular diseases are very crucial for diagnosis and management process. Biomarker detection demand is opened the important way in biosensor development field. Rapid, cheap, portable, precise, selective and sensitive biomarker sensing devices are needed at this point to detect and predict disease. A cardiac biomarker can be orderable as C-reactive protein, troponin I or T, myoglobin, tumor necrosis factor alpha, interleukin-6, interleukin-1, lipoprotein-associated phospholipase, low-density lipoprotein and myeloperoxidase. They are used for prediction of cardiovascular diseases. There are many methods for early diagnosis of cardiovascular diseases, but these have long time process and expensive devices. In recent studies, different biosensors have been developed to remove the problems in this field. Electrochemical devices and developed biosensors have many superiorities than others such as low cost, mobile, reliable, repeatable, need a little amount of solution. In this review, recent studies were presented as details for cardiovascular disease biomarkers detection using electrochemical methods.

Recent Advances in Electrochemical Immunosensors

Immunosensors have experienced a very significant growth in recent years, driven by the need for fast, sensitive, portable and easy-to-use devices to detect biomarkers for clinical diagnosis or to monitor organic pollutants in natural or industrial environments. Advances in the field of signal amplification using enzymatic reactions, nanomaterials such as carbon nanotubes, graphene and graphene derivatives, metallic nanoparticles (gold, silver, various oxides or metal complexes), or magnetic beads show how it is possible to improve collection, binding or transduction performances and reach the requirements for realistic clinical diagnostic or environmental control. This review presents these most recent advances; it focuses first on classical electrode substrates, then moves to carbon-based nanostructured ones including carbon nanotubes, graphene and other carbon materials, metal or metal-oxide nanoparticles, magnetic nanoparticles, dendrimers and, to finish, explore the use of ionic liquids. Analytical performances are systematically covered and compared, depending on the detection principle, but also from a chronological perspective, from 2012 to 2016 and early 2017.

Electrochemical immunosensor for simultaneous determination of interleukin-1 beta and tumor necrosis factor alpha in serum and saliva using dual screen printed electrodes modified with functionalized double-walled carbon nanotubes

Dual screen-printed carbon electrodes modified with 4-carboxyphenyl-functionalized double-walled carbon nanotubes (HOOC-Phe-DWCNTs/SPCEs) have been used as scaffolds for the preparation of electrochemical immunosensors for the simultaneous determination of the cytokines Interleukin-1β (IL-1β) and factor necrosis tumor α (TNF-α). IL-1β. Capture antibodies were immobilized onto HOOC-Phe-DWCNTs/SPCEs in an oriented form making using the commercial polymeric coating Mix&Go™. Sandwich type immunoassays with amperometric signal amplification through the use of poly-HRP-streptavidin conjugates and H₂O₂ as HRP substrate and hydroquinone as redox mediator were implemented. Upon optimization of the experimental variables affecting the immunosensor performance, the dual immunosensor allows ranges of linearity extending between 0.5 and 100 pg/mL and from 1 to 200 pg/mL for IL-1β and TNF-α, respectively, these ranges being adequate for the determination of the cytokines in clinical samples. The achieved limits of detection were 0.38 pg/mL (IL-1β) and 0.85 pg/mL (TNF-α). In addition, the dual immunosensor exhibits excellent reproducibility of the measurements, storage stability of the anti-IL-Phe-DWCNTs/SPCE and anti-TNF-Phe-DWCNTs/SPCE conjugates, and selectivity as well as negligible cross-talking. The dual immunosensor was applied to the simultaneous determination of IL-1β and TNF-α in human serum spiked at clinically relevant concentration levels and in real saliva samples.

Enzymatically catalytic signal tracing by a glucose oxidase and ferrocene dually functionalized nanoporous gold nanoprobe for ultrasensitive electrochemical measurement of a tumor biomarker

A nanoporous gold nanosphere (pAu NS) was synthesized to load high-content glucose oxidase (GOx) and ferrocene (Fc) for the successful preparation of a new gold nanoprobe. After the specific recognition of the tumor biomarker of carcinoembryonic antigen (CEA) at a gold electrode based aptasensor, this GOx and Fc dually functionalized pAu NS nanoprobe was further used for sandwich immunoreaction and signal tracing. Based on the Fc-mediated GOx-catalytic reaction, the gold nanoprobes quantitatively captured onto the electrode surface produced a sensitive electrochemical signal corresponding to the protein recognition events, which led to the development of a new biosensing method for CEA measurement. Both the high loading of GOx and Fc on the pAu NS nanocarrier and the enzymatically catalytic reaction of the nanoprobe greatly amplify the electrochemical signal; meanwhile, the immobilization of the Fc mediator on this enzyme nanoprobe and the highly specific aptamer recognition drastically decrease the background current, resulting in the achievement of ultrahigh sensitivity of the method. Under optimum conditions, this method shows an excellent analytical performance including a wide linear relationship of five-order of magnitude and a low detection limit down to 0.45 pg mL(-1). Thus this pAu NS based gold nanoprobe and the proposed immunoassay method provide great potential for practical applications.

Peptide-Modulated Self-Assembly of Chromophores toward Biomimetic Light-Harvesting Nanoarchitectonics

Elegant self-assembling complexes by the combination of proteins/peptides with functional chromophores are decisively responsible for highly efficient light-harvesting and energy transfer in natural photosynthetic systems. Mimicking natural light-harvesting complexes through synthetic peptides is attractive due to their advantanges of programmable primary structure, tunable self-assembly architecture and easy availability in comparison to naturally occuring proteins. Here, an overview of recent progresses in the area of biomimetic light-harvesting nanoarchitectonics based on peptide-modulated self-assembly of chromophores is provided. Adjusting the organization of chromophores, either by creating peptide-chromophore conjugates or by the non-covalent assembly of peptides and chromophores are highlighted. The light-harvesting properties, especially the energy transfer of the biomimetic complexes are critically discussed. The applications of such complexes in the mineralization of inorganic nanoparticles, generation of molecular hydrogen and oxygen, and photosynthesis of bioactive molecules are also included.

Strategies for the development of an electrochemical bioassay for TNF-alpha detection by using a non-immunoglobulin bioreceptor

TNF-α is an inflammatory cytokine produced by the immune system. Serum TNF-α level is elevated in some pathological states such as septic shock, graft rejection, HIV infection, neurodegenerative diseases, rheumatoid arthritis and cancer. Detecting trace amount of TNF-α is, also, very important for the understanding of tumor biological processes. Detection of this key biomarker is commonly achieved by use of ELISA or cytofluorimetric based methods. In this study the traditional optical detection was replaced by differential pulse voltammetry (DPV) and an affinity molecule, produced by evolutionary approaches, has been tested as capture bioreceptor. This molecule, namely a combinatorial non-immunoglobulin protein (Affibody®) interacts with TNF-α selectively and was here tested in a sandwich assay format. Moreover magnetic beads were used as support for bioreceptor immobilization and screen printed carbon electrodes were used as transducers. TNF-α calibration curve was performed, obtaining the detection limit of 38pg/mL, the quantification range of 76-5000pg/mL and RSD%=7. Preliminary results of serum samples analysis were also reported.

A robust electrochemiluminescence immunoassay for carcinoembryonic antigen detection based on a microtiter plate as a bridge and Au@Pd nanorods as a peroxidase mimic

The common drawbacks of most traditional electrochemiluminescence (ECL) immunoassays are the strict storage conditions for the ECL electrode and the steric hindrance caused by bovine serum albumin and antigen.

Synthesis and electrocatalytic effect of Ag@Pt core-shell nanoparticles supported on reduced graphene oxide for sensitive and simple label-free electrochemical aptasensor

Bimetallic Ag@Pt core-shell nanoparticles supported on reduced graphene oxide nanosheets (Ag@Pt-GRs) was synthesized and used as novel desirable sensor platform and electrocatalyst for catechol as probe in aptasensor. Gold screen-printed electrodes modified with Ag@Pt-GRs and applied to advance enzyme-free and label-free electrochemical aptasensor for detection of protein biomarker tumor necrosis factor-alpha (TNF-α). The morphology of the Ag@Pt-GRs could be characterized by transmission electron microscopy, X-ray diffraction and UV-vis spectra. The results showed that these nanocomposite exhibited attractive electrocatalytic activity and also yielded large surface area, which improve the amount of immobilized TNF-α aptamer. Due to the excellent electrocatalytic activity of Ag@Pt-GRs towards the oxidation of catechol, determination of TNF-α antigen was based on its obstruction to the electrocatalytic oxidation of catechol by Ag@Pt-GRs after binding to the surface of electrode through interaction with the aptamer. The calibration curve was obtained by differential pulse voltammetry and square wave voltammetry. Under optimum conditions, the results demonstrated that this electrochemical aptasensor possessed a dynamic range from 0.0 pg/mL to 60 pg/mL with a low detection limit of 2.07 pg/mL for TNF-α. The analytical usefulness of the aptasensor was finally demonstrated analyzing serum samples. The simple fabrication method, high sensitivity, specificity, good reproducibility and stability as well as acceptable accuracy for TNF-α detection in human serum samples are the main advantages of this aptasensor, which might have broad applications in protein diagnostics and bioassay.

Hyperbranched rolling circle amplification based electrochemiluminescence aptasensor for ultrasensitive detection of thrombin

An ultrasensitive electrochemiluminescence (ECL) aptamer sensor for protein (thrombin as an example) detection based on hyperbranched rolling circle amplification (HRCA) had been developed. A complementary single-strand DNA (CDNA) of the thrombin aptamer had been modified on the gold electrode firstly, and then hybridized with thrombin aptamer to make the aptamer immobilized on the electrode surface, in the presence of thrombin, aptamer-thrombin bioaffinity complexes formed and made thrombin aptamer leave the electrode surface. Thus, the linear padlock probe hybridized with the free CDNA on the electrode surface and circularized by Escherichia coli DNA ligase. Subsequently, the linear padlock probe was served as a template for the initiation of HRCA reaction, and a lot of dsDNA modified on the electrode surface. Then Ru(phen)₃²⁺ (acted as the ECL indicator) intercalates specifically into double-stranded DNA (dsDNA) grooves to generate ECL signal. The ECL intensity of the system has a linear relationship with thrombin concentration in the range of 3.0-300 aM with a detection limit of 1.2 aM (S/N=3). The proposed method combines the high sensitivity of ECL, exponential amplification of HRCA for signal enhancement and high selectivity of aptamer.

Amperometric magnetoimmunoassay for the direct detection of tumor necrosis factor alpha biomarker in human serum

An amperometric immunoassay for the determination of tumor necrosis factor alpha (TNFα) protein biomarker in human serum based on the use of magnetic microbeads (MBs) and disposable screen-printed carbon electrodes (SPCEs) has been developed. The specifically modified microbeads were magnetically captured on the working electrode surface and the amperometric responses were measured at -0.20V (vs. Ag pseudo-reference electrode), upon addition of hydroquinone (HQ) as electron transfer mediator and H2O2 as the enzyme substrate. After a thorough optimization of the assay, extremely low limits of detection were achieved: 2.0pg mL(-1) (36fM) and 5.8pg mL(-1) (105fM) for standard solutions and spiked human serum, respectively. The simplicity, robustness and this clinically interesting LOD proved the developed TNFα immunoassay as a good contender for real clinical application.

An ultrasensitive colorimetric aptasensor for ATP based on peptide/Au nanocomposites and hemin–G-quadruplex DNAzyme

A self-assembled peptide nanosphere was firstly applied to construct biosensors. A new signal amplification strategy was proposed for colorimetric aptasensor based on PNS/AuNPs composite. The colorimetric aptasensor displayed an ultra-high sensitivity for ATP detection with a LOD of 1.35 pM.

Highly enhanced electrochemiluminescence based on pseudo triple-enzyme cascade catalysis and in situ generation of co-reactant for thrombin detection

In this work, a novel pseudo triple-enzyme cascade catalysis amplification strategy was employed to fabricate a highly sensitive electrochemiluminescence (ECL) aptasensor for thrombin (TB) detection.

Paper based colorimetric biosensing platform utilizing cross-linked siloxane as probe

Paper based colorimetric biosensing platform utilizing cross-linked siloxane 3-aminopropyltriethoxysilane (APTMS) as probe was developed for the detection of a broad range of targets including H2O2, glucose and protein biomarker. APTMS was extensively used for the modification of filter papers to develop paper based analytical devices. We discovered when APTMS was cross-linked with glutaraldehyde (GA), the resulting complex (APTMS-GA) displays brick-red color, and a visual color change was observed when the complex reacted with H2O2. By integrating the APTMS-GA complex with filter paper, the modified paper enables quantitative detection of H2O2 through the monitoring of the color intensity change of the paper via software Image J. Then, with the immobilization of glucose oxidase (GOx) onto the modified paper, glucose can be detected through the detection of enzymatically generated H2O2. For protein biomarker prostate specific antigen (PSA) assay, we immobilized capture, not captured anti-PSA antibody (Ab1) onto the paper surface and using GOx modified gold nanorod (GNR) as detection anti-PSA antibody (Ab2) label. The detection of PSA was also achieved via the liberated H2O2 when the GOx label reacted with glucose. The results demonstrated the possibility of this paper based sensor for the detection of different analytes with wide linear range. The low cost and simplicity of this paper based sensor could be developed for "point-of-care" analysis and find wide application in different areas.

A signal amplification strategy using the cascade catalysis of gold nanoclusters and glucose dehydrogenase for ultrasensitive detection of thrombin

This work reports a novel signal amplification strategy for ultrasensitive detection of thrombin by cascade catalysis of gold nanoclusters (AuNCs) and glucose dehydrogenase (GDH). Herein, the AuNCs prepared by using polyamidoamine dendrimer as template were constructed not only as nanocarriers for anchoring the large amounts of secondary thrombin aptamers but also as nanocatalysts to catalyze the oxidation of NADH efficiently. Moreover, a large amount of GDH was loaded through the immobilization technology of DNA hybridization and a large amount of toluidine blue (Tb) was intercalated into the DNA grooves via electrostatic interaction. Significantly, the electrochemical signal was greatly enhanced based on cascade catalysis: firstly, GDH catalyzed the oxidation of glucose to gluconolactone with the concomitant generation of NADH in the presence of NAD(+). Then, AuNCs as nanocatalysts could effectively catalyze NADH to produce NAD(+) with the help of Tb as redox probe. Under the optimal conditions, the proposed aptasensor exhibits a linear range of 1.0×10(-14)-5×10(-9) M with a low detection limit of 3.3×10(-15) M for thrombin detection and shows high sensitivity and good specificity.

A sensitive NADH and ethanol biosensor based on graphene-Au nanorods nanocomposites

In this paper, a simple strategy for the synthesis of graphene-Au nanorods hybrid nanosheets (GN-AuNRs) through electrostatic interaction has been demonstrated. Due to the synergistic effect between AuNRs and GN, the hybrid nanosheets exhibited excellent performance toward dihydronicotinamide adenine dinucleotide (NADH) oxidation, with a low detection limit of 6 µM. The linear GN-AuNRs also served as a biocompatible and electroactive matrix for enzyme assembly to facilitate the electron transfer between the enzyme and the electrode. Using alcohol dehydrogenase (ADH) as a model system, a simple and effective sensing platform was developed for ethanol assay. The response displayed a good linear range from 5 to 377 µM with detection limit 1.5 μM. Furthermore, the interference effects of redox active substances, such as uric acid, ascorbic acid and glucose for the proposed biosensor were negligible.