Multiplexed Electrochemical Immunoassay of Phosphorylated Proteins Based on Enzyme-Functionalized Gold Nanorod Labels and Electric Field-Driven Acceleration

Efficiency of electrochemical immuno- vs. apta(geno)sensors for multiple cancer biomarkers detection

The interest in biosensors technology has been constantly growing over the last few years. It is still the biggest challenge to design biosensors able to detect two or more analytes in a single measurement. Electrochemical methods are frequently used for this purpose, mainly due to the possibility of applying two or more different redox labels characterized by independent and distinguished electrochemical signals. In addition to antibodies, nucleic acids (aptamers) have been increasingly used as bioreceptors in the construction of such sensors. Within this review paper, we have collected the examples of electrochemical immuno- and geno(apta)sensors for simultaneous detection of multiple analytes. Based on many published literature examples, we have emphasized the recent application of multiplexed platforms for detection of cancer biomarkers. It has allowed us to compare the progress in design strategies, including novel nanomaterials and amplification of signals, to get as low as possible limits of detection. We have focused on multi-electrode and multi-label strategies based on redox-active labels, such as ferrocene, anthraquinone, methylene blue, thionine, hemin and quantum dots, or metal ions such as Ag+, Pb2+, Cd2+, Zn2+, Cu2+ and others. We have finally discussed the possible way of development, challenges and prospects in the area of multianalyte electrochemical immuno- and geno(apta)sensors.

Integrating of analytical techniques with enzyme-mimicking nanomaterials for the fabrication of microfluidic systems for biomedical analysis

Bioanalysis faces challenges in achieving fast, reliable, and point-of-care (POC) determination methods for timely diagnosis and prognosis of diseases. POC devices often display lower sensitivity compared to laboratory-based methods, limiting their ability to quantify low concentrations of target analytes. To enhance sensitivity, the synthesis of new materials and improvement of the efficiency of the analytical strategies are necessary. Enzyme-mimicking materials have revolutionized the field of the fabrication of new high-throughput sensing devices. The integration of microfluidic chips with analytical techniques offers several benefits, such as easy miniaturization, need for low biological sample volume, etc., while also enhancing the sensitivity of the probe. The use enzyme-like nanomaterials in microfluidic systems can offer portable strategies for real-time and reliable detection of biological agents. Colorimetry and electrochemical methods are commonly utilized in the fabrication of nanozyme-based microfluidic systems. The review summarizes recent developments in enzyme-mimicking materials-integrated microfluidic analytical methods in biomedical analysis and discusses the current challenges, advantages, and potential future directions.

Multiplex Aptamer-Based Fluorescence Assay Using Magnetism-Encoded Nanoparticles for Simultaneous Detection of Multiple Pathogenic Bacteria

Multiplex assay has emerged as a robust and versatile method for the simultaneous detection of multiple analytes in a single test. However, challenges in terms of poor accuracy and complexity remained. In this work, we developed a multiplex aptamer-based fluorescence assay using magnetism-encoded nanoparticles for the simultaneous detection of multiple pathogenic bacteria. The encapsulation of different amounts of Fe3O4 nanoparticles in zeolitic imidazolate framework-90 (ZIF-90) leads to the formation of Fe3O4@ZIF-90 (FZ) composites with distinct magnetism strengths. By functionalizing a specific aptamer on the surface of the FZ composites, target bacteria can be specifically and precisely separated from a mixed sample in a sequential manner. This property allows for the simultaneous quantitative analysis of multiple target bacteria by using a single-color fluorescence label, thereby resulting in minimal spectral crosstalk interference and improved accuracy. The successful determination of multiple bacteria in contaminated milk samples demonstrates the applicability of this multiplex assay in complex biological matrices. Compared to conventional multiplex fluorescence assays, this approach offers distinct advantages of simplicity, efficiency, and implementation. We believe that this study can provide valuable insights into the development of the multiplex assay while introducing a new method for the simultaneous detection of multiple bacteria.

Nanomaterials-enriched sensors for detection of chiral pharmaceuticals

Advancements in nanoscience and nanotechnology have opened new pathways to fabricate novel nanostructures with interesting properties that would be used for different applications. In this respect, nanostructures comprising chirality are one of the most rapidly developing research fields encompassing chemistry, physics and biology. Chirality, also known as mirror asymmetry, describes the geometrical property of an object that is not superimposable on its mirror image. This characteristic plays a crucial role because these identical forms of chiral species in pharmaceuticals or food additives may exhibit different effects on living organisms. Therefore, chiral analysis is an important field of modern chemical analysis in health-related industries that are reliant on the production of enantiomeric compounds involving pharmaceuticals. This review covers the recent advances dealing with the synthesis, design and advantageous analytical performance of nanomaterials-enriched sensors used for chiral pharmaceuticals. We conclude this review with the challenges existing in this research field and our perspectives on some potential strategies with cutting-edge approaches for the rational design of sensors for chiral pharmaceuticals. We expect this comprehensive review will inspire future studies in nanomaterials-enriched chiral sensors.

Ultrafast Electrothermal Flow-Enhanced Magneto Biosensor for Highly Sensitive Protein Detection in Whole Blood

Current diagnostic tests for sensitive protein detection rely on immunological techniques, such as ELISA, which require sample purification, multiple washing steps and lengthy incubation, hindering their use for rapid testing. Here, we report a simple electrothermal flow-enhanced biosensor for ultrafast, high sensitivity measurements of protein biomarkers in whole blood. Magnetic nanobeads dually-labeled with a detection antibody and enzyme reporter are used to form immunocomplexes with the target protein, which are readily transported to the sensor via magnetic concentration. The incorporation of electrothermal flows enhances immunocomplex formation, allowing for rapid and sensitive detection without requiring blood purification or lengthy incubation. Proof of concept was carried out using Plasmodium falciparum histidine-rich protein 2 (PfHRP2), a malaria parasite biomarker, which could be detected at concentrations as low as 5.7 pg mL-1 (95 fM) in whole blood in 7 min. The speed, sensitivity and simplicity of this device make it attractive for rapid diagnostic testing.

Monolithic integration of nanorod arrays on microfluidic chips for fast and sensitive one-step immunoassays

Here, we present integrated nanorod arrays on microfluidic chips for fast and sensitive flow-through immunoassays of physiologically relevant macromolecules. Dense arrays of Au nanorods are easily fabricated through one-step oblique angle deposition, which eliminates the requirement of advanced lithography methods. We report the utility of this plasmonic structure to improve the detection limit of the cardiac troponin I (cTnI) assay by over 6 × 105-fold, reaching down to 33.9 fg mL-1 (~1.4 fM), compared with an identical assay on glass substrates. Through monolithic integration with microfluidic elements, the device enables a flow-through assay for quantitative detection of cTnI in the serum with a detection sensitivity of 6.9 pg mL-1 (~0.3 pM) in <6 min, which was 4000 times lower than conventional glass devices. This ultrasensitive detection arises from the large surface area for antibody conjugation and metal-enhanced fluorescent signals through plasmonic nanostructures. Moreover, due to the parallel arrangement of flow paths, simultaneous detection of multiple cancer biomarkers, including prostate-specific antigen and carcinoembryonic antigen, has been fulfilled with increased signal-to-background ratios. Given the high performance of this assay, together with its simple fabrication process that is compatible with standard mass manufacturing techniques, we expect that the prepared integrated nanorod device can bring on-site point-of-care diagnosis closer to reality.

Adriamycin coated silica microspheres as labels for cancer biomarker alpha-fetoprotein detection

Adriamycin (ADM)-coated silica microspheres as a label for the sensitive detection of a cancer biomarker alpha-fetoprotein (AFP) was reported. Silica microspheres (SiO2 MSs) were employed as the carrier for the immobilization of gold nanoparticles (Au NPs), secondary antibody (Ab2) and ADM (denote: ADM@Au NPs@SiO2 MS/Ab2) as labels. In the presence of AFP, the labels were captured on the surface of the Au NP-reduced graphene oxide (rGO) (Au NP-rGO) nanocomposites to form a sandwich structure vs. the specific recognition of antibody-antigen. In a pH 7.4 phosphate buffer solution, a well-defined peak of ADM at about -0.70 V (vs. SCE) was recorded via differential pulse voltammetry, the peak intensity of which was related to the concentration of AFP. Under optimal experimental conditions, the immunoassay exhibited a wide linear range (0.5 pg mL-1 to 75 ng mL-1) and low limit of detection (0.17 pg mL-1). Further, the immunoassay was evaluated for serum samples, which gave satisfactory results.

Disposable multiplexed electrochemical sensors based on electro-triggered selective immobilization of probes for simultaneous detection of DNA and proteins

Electrically addressable covalent immobilization of probes on a multiplexed electrode for the simultaneous detection of multiple targets within the same sample is often regarded as a difficult milestone to be achieved. Herein, we demonstrated a reagentless disposable multiplexed electrochemical DNA and aptamer-based sensing platform for the simultaneous determination of various targets. The electrochemically triggered "click" chemistry was developed, and three biomarkers, including p53, thrombin, and VEGF165 were used as model analytes. The proposed sensor consisted of three independent screen-printed carbon electrodes (SPCE), with an alkyne-azide cycloaddition reaction that was activated selectively by means of electrical triggering, so that different DNA probes can be modified on the desired electrode units in sequence. In terms of simultaneous detection, the sensor was able to quantify the DNA target of p53 with a detection limit of 0.35 nM, whereas the limits of detection for protein quantification of thrombin and VEGF165 were 0.22 nM and 0.014 nM, respectively. The proposed sensor not only showed encouraging reproducibility and stability, but also performed well even in 50% serum samples. Therefore, the work described here offers a general strategy for developing a multiplexed sensor with promising potential to achieve rapid, simple and cost-effective analysis of biological samples.

Fabrication of a sensitive label free electrochemical immunosensor for detection of prostate specific antigen using functionalized multi-walled carbon nanotubes/polyaniline/AuNPs

The aim of this research is to introduce a novel label free electrochemical immunosensor based on glassy carbon electrode (GCE) modified with carboxylated carbon nanotubes (COOH-MWCNTs)/polyaniline (PANI)/gold nanoparticles (AuNPs) for the detection of prostate specific antigen (PSA). The AuNPs were utilized as a connector for PSA antibody immobilization through NH₂ groups on antibody. Investigations on modified electrode surface were performed by FT-IR spectrum, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) to evaluate the synthesized nanocomposite and modified electrode surface. As a sensitive analytical method for the detection of PSA, differential pulse voltammetry (DPV) was employed in different ranges of antigen concentration, 1.66 ag·mL^-1 to 1.3 ng·mL^-1. In addition, the detection limit was obtained 0.5 pg·mL^-1, from the linear relationship between antigen concentration log and peak current. Also, the proposed immunosensor was carried out for the determination of PSA in human serum samples, indicating recoveries ranging from 92 to 104%. Finally, it should be noted that the reproducibility and specificity, along with the stability of the present immunosensor were examined, and satisfactory findings were obtained, thus proving it as a promising PSA immunosensor.

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.

Low-Cost Localized Surface Plasmon Resonance Biosensing Platform with a Response Enhancement for Protein Detection

There are many potential applications for biosensors that can provide real-time analysis, such as environmental monitoring and disease prevention. In this study, we investigated a simple strategy for real-time protein detection, which had the advantages of affordability, fast response, portability, and ease of use. A robust quantification of protein interaction was achieved by combining capillary localized surface plasmon resonance (LSPR) sensors and complementary metal–oxide–semiconductor (CMOS) image sensors. Gold nanoparticles were modified on the inner wall of the capillary, which was used as a microfluidic channel and sensing surface. We functionalized one of the LSPR sensors using ligand bound to gold nanoparticle. Our proposed biosensing platform could be easily multiplexed to achieve high throughput screening of biomolecular interactions, and it has the potential for use in disposable sensors. Moreover, the sensing signal was enhanced by the extinction effect of gold nanoparticles. The experimental results showed that our device could achieve qualitative identification and quantitative measurement of transferrin and immunoglobulin G (IgG). As a field-portable and low-cost optical platform, the proposed LSPR biosensing device is broadly applicable to various protein binding tests via a similar self-assembly of organic ultrathin films.

Simultaneous determination of two phosphorylated p53 proteins in SCC-7 cells by an ICP-MS immunoassay using apoferritin-templated europium(III) and lutetium(III) phosphate nanoparticles as labels

Phosphorylated p53 proteins are biomarkers with clinical utility for early diagnosis of cancer, but difficult to quantify. An inductively coupled plasma mass spectrometry (ICP-MS) based immunoassay is described here that uses uniform lanthanide nanoparticles (NPs) as elemental tags for the simultaneous determination of two phosphorylated p53 proteins. Apoferritin templated europium (Eu) phosphate (AFEP) NPs and apoferritin templated lutetium (Lu) phosphate (AFLP) NPs with 8 nm in diameter were used to label two phosphorylated p53 proteins at serine 15 and serine 392 sites (p-p53¹⁵ and p-p53³⁹²), respectively. The assay has a sandwich format, and p-p53¹⁵ and p-p53³⁹² were first captured and then recognized by AFEP and AFLP NPs labelled antibodies, respectively. The Eu and Lu were then released from the immune complexes under acidic condition for ICP-MS measurement. The limits of detection for p-p53¹⁵ and p-p53³⁹² are 200 and 20 pg·mL^-1, with linear ranges of 0.5-20 and 0.05-20 ng·mL^-1, respectively. The method was further applied to study the response of p-p53¹⁵ and p-p53³⁹² in SCC-7 cells exposed to the natural carcinogen arsenite. A significant up-regulation of p-p53¹⁵ and p-p53³⁹² can be observed when cells were exposed to arsenite at 5 μmol·L^-1 level for 24 h. Graphical abstract Schematic presentation of the ICP-MS immunoassay using apoferritin templated europium (III) and lutetium (III) phosphate nanoparticles as labels for the simultaneous determination of two phosphorylated p53 proteins. Europium (Eu) phosphate nanoparticles (blue) and lutetium (Lu) phosphate nanoparticles (pink) were synthesized in the size-restricted cavity of apoferritin. They were further coupled with antibodies to prepare Eu and Lu labelled probes for p-p53¹⁵ (blue) and p-p53³⁹² (pink), respectively. After formation of a a sandwich, the labelled Eu and Lu were dissociated in acid and then introduced to ICP-MS for the simultaneous determination of two phosphorylated p53 proteins p-p53¹⁵ (blue) and p-p53³⁹² (pink).

The Advent of Salivary Breast Cancer Biomarker Detection Using Affinity Sensors

Breast Cancer is one of the world's most notorious diseases affecting two million women in 2018 worldwide. It is a highly heterogeneous disease, making it difficult to treat. However, its linear progression makes it a candidate for early screening programs, and the earlier its detection the higher the chance of recovery. However, one key hurdle for breast cancer screening is the fact that most screening techniques are expensive, time-consuming, and cumbersome, making them impractical for use in several parts of the world. One current trend in breast cancer detection has pointed to a possible solution, the use of salivary breast cancer biomarkers. Saliva is an attractive medium for diagnosis because it is readily available in large quantities, easy to obtain at low cost, and contains all the biomarkers present in blood, albeit in lower quantities. Affinity sensors are devices that detect molecules through their interactions with biological recognition molecules. Their low cost, high sensitivity, and selectivity, as well as rapid detection time make them an attractive alternative to traditional means of detection. In this review article, we discuss the current status of breast cancer diagnosis, its salivary biomarkers, as well as the current trends in the development of affinity sensors for their detection.

Real-time surface plasmon resonance monitoring of site-specific phosphorylation of p53 protein and its interaction with MDM2 protein

Real-time monitoring of site-specific phosphorylation of p53 protein and its binding to MDM2 is conducted using dual-channel surface plasmon resonance (SPR).

Enzymatic Nanocomposites with Radio Frequency Field-Modulated Activity

The control over enzymatic activity by physical stimuli is of interest to many applications in medicine, biotechnology, synthetic biology, and nanobionics. Although the main focus has been on optically responsive systems, alternative strategies to modulate the enzymatic activity of hybrid systems are needed. Here we describe a radiofrequency (RF) field controlled catalytic activity of an enzymatic sol-gel composite. Specifically, the activity of bovine carbonic anhydrase entrapped in sol-gel-derived magnetite (enzyme@ferria) composite was accelerated by a factor of 460% compared to its initial value, by applying the RF field of 937 A/m, with fast response time. This acceleration is reversible and its magnitude controllable. An acceleration mechanism, based on RF-induced heating of the magnetite by the Néel relaxation effect, is proposed and proven. The entrapment within a sol-gel matrix solves the problem of enhancing activity by heating without denaturing the enzyme. RF-controlled enzymatic composites can be potentially applied as biological RF sensors or to control biochemical reactions within living organisms.

Fiber Light-Coupled Optofluidic Waveguide (FLOW) Immunosensor for Highly Sensitive Detection of p53 Protein

Highly sensitive detection of molecular tumor markers is essential for biomarker-based cancer diagnostics. In this work, we showcase the implementation of fiber light-coupled optofluidic waveguide (FLOW) immunosensor for the detection of p53 protein, a typical tumor marker. The FLOW consists of a liquid-core capillary and an accompanying optical fiber, which allows evanescent interaction between light and microfluidic sample. Molecular binding at internal surface of the capillary induces a response in wavelength shift of the transmission spectrum in the optical fiber. To enable highly sensitive molecular detection, the evanescent-wave interaction has been strengthened by enlarging shape factor R via fine geometry control. The proposed FLOW immunosensor works with flowing microfluid, which increases the surface molecular coverage and improves the detection limit. As a result, the FLOW immunosensor presents a log-linear response to the tumor protein at concentrations ranging from 10 fg/mL up to 10 ng/mL. In addition, the nonspecifically adsorbed molecules can be effectively removed by the fluid at an optimal flow rate, which benefits the accuracy of the measurement. Tested in serum samples, the FLOW successfully maintains its sensitivity and specificity on p53 protein, making it suitable for diagnostics applications.

Improved screen-printed carbon electrode for multiplexed label-free amperometric immuniosensor: Addressing its conductivity and reproducibility challenges

A new screen-printed carbon electrode (SPCE) with multiple working electrodes and one signal output channel without counter and reference electrodes was designed. The multiple working electrodes can be individually modified for each target of interest. The SPCE contained one signal output channel, making the immuniosensor be realized by common single-channel electrochemical workstation. The counter and reference electrodes were independent of disposable SPCE, reducing costs and eliminating precious metal pollution. Platinum network as counter electrode improved the reproducibility of the SPCE. Moreover, method of generating hydrogel on working electrode was used to enhance the conductivity of SPCE. Based on this, a multiplexed single channel label-free amperometric immuniosensor for four tumor markers, namely, squamous cell carcinoma antigen (SCCA), fragment antigen 21-1 (Cyfra21-1), carbohydrate antigen 125 (CA125), and neuron specific enolase (NSE) was developed, and the corresponding detection limits were 5.5pgmL^-1, 4.8pgmL^-1, 0.0054UmL^-1 and 2.3pgmL^-1, respectively. The sensitivity of this immunosensor was 0.83µA (lg(ngmL^-1))^-1 for SCCA, 1.92µA (lg(ngmL^-1))^-1 for Cyfra21-1, 4.75µA (lg(UmL^-1))^-1 for CA125 and 2.40µA (lg(ngmL^-1))^-1 for NSE. Among them, the sensitivities of CA125 and NSE were four-fold higher than those of the previous works.

An innovative immunosensor for detection of tumor suppressor protein p53 in unprocessed human plasma and cancer cell lysates

An innovative mediator-free electrochemical immunosensor for quantitation of p53 tumor suppressor protein based on signal amplification strategy was fabricated. In this work, biotin conjugated p53-antibody (anti-p53) was immobilized onto a green and biocompatible nanocomposite containing poly l-cysteine (P-Cys) as conductive matrix and 3D gold nanoparticles (GNPs) as signal amplification element. Therefore, a novel nanocomposite film based on P-Cys and GNPs was exploited to develop a highly sensitive immunosensor for detection of p53 protein. Importantly, GNPs prepared by sonoelectrodeposition method which lead to compact morphology. Fully electrochemical methodology was used to prepare a new transducer on a gold surface which provided a high surface area to immobilize a high amount of the anti-p53. The surface morphology of electrode was characterized by high-resolution field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDX). The immunosensor was employed for the detection of p53 in physiological pH using square wav voltammetry and differential pulse voltammetry (DPVs) techniques. Under optimized condition the calibration curve for p53 concentration by SWV and DPV was linear in 0.0369-50pM and 0.018-2.5pM with lower limit of quantification of 48fM and 18fM, respectively. The method was successfully applied assay of the p53 in unprocessed human plasma samples. Also, the method was applied to the assay of p53 in human plasma sample and normal and malignant cell line lysates such as (L929 normal cell Line from mouse C3H (L929), colon cancer cell-HCT, prostate cancer cell line PC-3, and human breast adenocarcinoma cell line-MCF7).

Multiplexed Electrochemical Immunosensors for Clinical Biomarkers

Management and prognosis of disease requires the accurate determination of specific biomarkers indicative of normal or disease-related biological processes or responses to therapy. Moreover since multiple determinations of biomarkers have demonstrated to provide more accurate information than individual determinations to assist the clinician in prognosis and diagnosis, the detection of several clinical biomarkers by using the same analytical device hold enormous potential for early detection and personalized therapy and will simplify the diagnosis providing more information in less time. In this field, electrochemical immunosensors have demonstrated to offer interesting alternatives against conventional strategies due to their simplicity, fast response, low cost, high sensitivity and compatibility with multiplexed determination, microfabrication technology and decentralized determinations, features which made them very attractive for integration in point-of-care (POC) devices. Therefore, in this review, the relevance and current challenges of multiplexed determination of clinical biomarkers are briefly introduced, and an overview of the electrochemical immunosensing platforms developed so far for this purpose is given in order to demonstrate the great potential of these methodologies. After highlighting the main features of the selected examples, the unsolved challenges and future directions in this field are also briefly discussed.

Simultaneous detection of clenbuterol and ractopamine based on multiplexed competitive surface enhanced Raman scattering (SERS) immunoassay

In this work, we demonstrate a competitive surface-enhanced Raman scattering (SERS) immunoassay for multiplexed detection of clenbuterol and ractopamine.

Disposable Amperometric Immunosensor for the Determination of Human P53 Protein in Cell Lysates Using Magnetic Micro-Carriers

An amperometric magnetoimmunosensor for the determination of human p53 protein is described in this work using a sandwich configuration involving the covalent immobilization of a specific capture antibody onto activated carboxylic-modified magnetic beads (HOOC-MBs) and incubation of the modified MBs with a mixture of the target protein and horseradish peroxidase-labeled antibody (HRP-anti-p53). The resulting modified MBs are captured by a magnet placed under the surface of a disposable carbon screen-printed electrode (SPCE) and the amperometric responses are measured at −0.20 V (vs. an Ag pseudo-reference electrode), upon addition of hydroquinone (HQ) as a redox mediator and H₂O₂ as the enzyme substrate. The magnetoimmunosensing platform was successfully applied for the detection of p53 protein in different cell lysates without any matrix effect after a simple sample dilution. The results correlated accurately with those provided by a commercial ELISA kit, thus confirming the immunosensor as an attractive alternative for rapid and simple determination of this protein using portable and affordable instrumentation.

Multiplex Immunosensor Arrays for Electrochemical Detection of Cancer Biomarker Proteins

Measuring panels of protein biomarkers offer a new personalized approach to early cancer detection, disease monitoring and patients' response to therapy. Multiplex electrochemical methods are uniquely positioned to provide faster, more sensitive, point of care (POC) devices to detect protein biomarkers for clinical diagnosis. Nanomaterials-based electrochemical methods offer sensitivity needed for early cancer detection. This review discusses recent advances in multiplex electrochemical immunosensors for cancer diagnostics and disease monitoring. Different electrochemical strategies including enzyme-based immunoarrays, nanoparticle-based immunoarrays and electrochemiluminescence methods are discussed. Many of these methods have been integrated into microfluidic systems, but measurement of more than 2-4 protein markers in a small single serum sample is still a challenge. For POC applications, a simple, low cost method is required. Major challenges in multiplexed microfluidic immunoassays are reagent additions and washing steps that require creative engineering solutions. 3-D printed microfluidics and paper-based microfluidic devices are also explored.

Silver-functionalized g-C3N4 nanohybrids as signal-transduction tags for electrochemical immunoassay of human carbohydrate antigen 19-9

A simple and feasible electrochemical immunosensing platform was developed for highly efficient screening of a disease-related protein (human carbohydrate antigen 19-9, CA 19-9 used in this case) using silver-functionalized g-C3N4 nanosheets (Ag/g-C3N4) as signal-transduction tags. Initially, Ag/g-C3N4 nanohybrids were synthesized by combining thermal polymerization of the melamine precursor with the photo-assisted reduction method. Thereafter, the as-synthesized Ag/g-C3N4 nanohybrids were utilized for the labeling of the anti-CA 19-9 detection antibody by using a typical carbodiimide coupling method. The assay was carried out on a capture antibody-modified glassy carbon electrode in a sandwich-type detection mode. The detectable signal mainly derived from the voltammetric characteristics of the immobilized nanosilver particles on the g-C3N4 nanosheets within the applied potentials. Under the optimal conditions, the voltammetric peak currents increased with the increasing amount of target CA 19-9, and exhibited a wide linear range from 5.0 mU mL(-1) to 50 U mL(-1) with a detection limit of 1.2 mU mL(-1). Our strategy also displayed good reproducibility, precision and specificity. The results of the analysis of clinical serum specimens were in good accordance with the results obtained by an enzyme-linked immunosorbent assay (ELISA) method. The newly developed immunosensing system is promising for enzyme-free and cost-effective analysis of low-abundance proteins.

Optimized dendrimer-encapsulated gold nanoparticles and enhanced carbon nanotube nanoprobes for amplified electrochemical immunoassay of E. coli in dairy product based on enzymatically induced deposition of polyaniline

A highly sensitive immunosensor was reported for Escherichia coli assay in dairy product based on electrochemical measurement of polyaniline (PAn) that was catalytically deposited by horseradish peroxidase (HRP) labels. Herein, the immunosensor was developed by using poly(amidoamine) dendrimer-encapsulated gold nanoparticles (PAMAM(Au)) as sensing platform. Importantly, the optimal HAuCl4/PAMAM ratio was investigated to design the efficient PAMAM(Au) nanocomposites. The nanocomposites were proven to not only increase the amount of immobilized capture antibody (cAb), but also accelerate the electron transfer process. Moreover, the {dAb-CNT-HRP} nanoprobes were prepared by exploiting the amplification effect of multiwalled carbon nanotubes (CNTs) for loading detection antibody (dAb) and enormous HRP labels. After a sandwich immunoreaction, the quantitatively captured nanoprobes could catalyze oxidation aniline to produce electroactive PAn for electrochemical measurement. On the basis of signal amplification of the PAMAM(Au)-based immunosensor and the {dAb-CNT-HRP} nanoprobes, the proposed strategy exhibited a linear relationship between the peak current of PAn and the logarithmic value of E. coli concentration ranging from 1.0 × 10(2) to 1.0 × 10(6) cfu mL(-1) with a detection limit of 50 cfu mL(-1) (S/N=3), and the electrochemical detection of E. coli could be achieved in 3h. The electrochemical immunosensor was also used to determine E. coli in dairy product (pure fresh milk, infant milk powder, yogurt in shelf-life and expired yogurt), and the recoveries of standard additions were in the range of 96.8-108.7%. Overall, this method gave a useful protocol for E. coli assay with high sensitivity, acceptable accuracy and satisfying stability, and thus provided a powerful tool to estimate the quality of dairy product.

Affinity-Mediated Homogeneous Electrochemical Aptasensor on a Graphene Platform for Ultrasensitive Biomolecule Detection via Exonuclease-Assisted Target-Analog Recycling Amplification

As is well-known, graphene shows a remarkable difference in affinity toward nonstructured single-stranded (ss) DNA and double-stranded (ds) DNA. This property makes it popular to prepare DNA-based optical sensors. In this work, taking this unique property of graphene in combination with the sensitive electrochemical transducer, we report a novel affinity-mediated homogeneous electrochemical aptasensor using graphene modified glassy carbon electrode (GCE) as the sensing platform. In this approach, the specific aptamer-target recognition is converted into an ultrasensitive electrochemical signal output with the aid of a novel T7 exonuclease (T7Exo)-assisted target-analog recycling amplification strategy, in which the ingeniously designed methylene blue (MB)-labeled hairpin DNA reporters are digested in the presence of target and, then, converted to numerous MB-labeled long ssDNAs. The distinct difference in differential pulse voltammetry response between the designed hairpin reporters and the generated long ssDNAs on the graphene/GCE allows ultrasensitive detection of target biomolecules. Herein, the design and working principle of this homogeneous electrochemical aptasensor were elucidated, and the working conditions were optimized. The gel electrophoresis results further demonstrate that the designed T7Exo-assisted target-analog recycling amplification strategy can work well. This electrochemical aptasensor realizes the detection of biomolecule in a homogeneous solution without immobilization of any bioprobe on electrode surface. Moreover, this versatile homogeneous electrochemical sensing system was used for the determination of biomolecules in real serum samples with satisfying results.

3D ordered silver nanoshells silica photonic crystal beads for multiplex encoded SERS bioassay

3D ordered silver nanoshell silica photonic crystal beads as a novel encoded surface enhanced Raman scattering substrate are proposed for the development of highly efficient multiplex bioassays.

Simultaneous quantification of Escherichia coli O157:H7 and Shigella boydii using a visual-antibody-macroarray

Being high throughput, rapid, automated, economical, convenient to operate and highly sensitive, protein arrays have been widely used in the analysis of tumor markers and veterinary drug residues. Pathogenic microbes also can be detected qualitatively by DNA array or protein array; however, their high throughput detection and quantification remains a big obstacle. To evaluate the potentiality of protein arrays for multiple quantitative detection of microorganisms with naked eye examination without the help of any equipment, here we developed a visual-antibody-macroarray (VAMA) aiming at rapid and simultaneous quantification of Escherichia coli O157:H7 and Shigella boydii. The results show that this VAMA is highly specific and is able to distinguish mixed Escherichia coli O157:H7 and Shigella boydii synchronously. The detection limits are equivalent to 3.4 × 10(5) CFU mL(-1) and 3.2 × 10(5) CFU mL(-1), respectively, which conform to the results of plate counting and ELISA. Importantly, the examination can be solely performed with the naked eye. Therefore, we provide an easy, reliable and rapid method for quantitative analysis of microorganisms.

Ultrasensitive electrochemical immunosensor for PSA biomarker detection in prostate cancer cells using gold nanoparticles/PAMAM dendrimer loaded with enzyme linked aptamer as integrated triple signal amplification strategy

In the present study, a triple signal amplification strategy was developed for ultrasensitive immunosensing of prostate-specific antigen (PSA) tumor marker. The proposed system was achieved by modification of glassy carbon electrode with graphene oxide/chitosan film and covalently attached of monoclonal PSA antibody and thionine as redox probe onto the modified electrode surface. Then, immunosensing was completed using sandwich-type immunoreaction of the PSA-antigen between anti-PSA immobilized on the graphene/chitosan interface and PSA-aptamer. For improve the sensitivity, polyamidoamine dendrimer-encapsulated gold nanoparticles (AuNPs-PAMAM) was used for covalent attachment of PSA-aptamer and HRP linked aptamer (Au-PAMA/aptamer-HRP) as electrochemical label in the sandwich format and electrocatalytic reduction of H2O2 in the presence of enzymatically oxidized thionine was measured. Under optimized condition, the obtained detection limit and linear concentration range were 10 fg ml(-1)(S/N=3) and 0.1 pg ml(-1) to 90 ngml(-1) respectively, using differential pulse voltammetry as measuring technique. In addition, electrochemical impedance spectroscopy (EIS) was used as simple, rapid, low cost label free analytical technique for PSA measurement with detection limit of 5 pg ml(-1) at concentration range up to 35 ng ml(-1). Finally, the immunosensor is used to PSA detection in human serum and prostate tissue samples and the obtained result is well agreed with the values obtained by the standard ELISA method. The obtained results indicate the proposed immunosensor can be used for monitor the differences in PSA concentration in cancer tissue samples which holds great promise in clinical screening of cancer biomarkers.

Glucose encapsulating liposome for signal amplification for quantitative detection of biomarkers with glucometer readout

A new technology was developed to quantitatively detect a broad range of disease biomarkers and proven to be portable, economical, and conveniently accessible. Measurements were performed based on releasing encapsulated glucose from antibody-tagged liposomes and subsequently detecting the released glucose using a commercial personal glucose meter (GM). The innovative aspect of this approach lies in the quantification of target biomarkers through the detection of glucose, thus expanding the applicability of the GM by broadening the range of target biomarkers instead of detecting only one analyte, glucose. Because of the bilayer membrane of liposomes, which can accommodate tens of thousands of glucose molecules, the sensitivity was greatly enhanced by using glucose encapsulating liposomes as a signal output and an amplifier. Here, the model analyte, protein 53 phosphorylated on Serine 15 (phospho-p53(15)), was captured by primary antibodies bound on magnetic Fe3O4 nanoparticles and then recognized by reporting antibodies conjugated to glucose encapsulating liposomes. Finally, the target phospho-p53(15) was detected by lysing the bound liposomes to release the encapsulated glucose (4 × 10(5) glucose molecules per liposome), which is detected with the GM. This approach was demonstrated to be a universal technology that can be easily produced to quantify a wide variety of biomarkers in medical diagnostics, food safety, public health, and environmental monitoring. In the near future, it is expected that these sensors, in combination with a portable GM, can be used in many fields such as physicians' laboratories, hospitals and the common household.

Toward the development of smart and low cost point-of-care biosensors based on screen printed electrodes

Screen printing technology provides a cheap and easy means to fabricate disposable electrochemical devices in bulk quantities which are used for rapid, low-cost, on-site, real-time and recurrent industrial, pharmaceutical or environmental analyses. Recent developments in micro-fabrication and nano-characterization made it possible to screen print reproducible feature on materials including plastics, ceramics and metals. The processed features forms screen-printed disposable biochip (SPDB) upon the application of suitable bio-chemical recognition receptors following appropriate methods. Adequacy of biological and non-biological materials is the key to successful biochip development. We can further improve recognition ability of SPDBs by adopting new screen printed electrode (SPE) configurations. This review covers screen-printing theory with special emphasis on the technical impacts of SPE architectures, surface treatments, operational stability and signal sensitivity. The application of SPE in different areas has also been summarized. The article aims to highlight the state-of-the-art of SPDB at the laboratory scale to enable us in envisaging the deployment of emerging SPDB technology on the commercial scale.

Visual electrochemiluminescence detection of cancer biomarkers on a closed bipolar electrode array chip

This paper describes a novel electrochemiluminescence (ECL) imaging platform for simultaneous detection of cancer biomarkers based on a closed bipolar electrode (BPE) array. It consists of two separated channel arrays: detection channel array and sensing channel array, which are connected by a group of parallel ITO BPEs on a glass substrate. Besides, two parallel ITO strips are fabricated at the two sides of BPE array and employed as driving electrodes. After Au films are electrochemically deposited on the cathodes of the BPE array, nanobioprobes including biorecognition elements (aptamer or antibody) and a novel electrochemical tag, which is synthesized by doping thionine in silica nanoparticles (Th@SiO2 NPs), are introduced into the cathodes by immunoreaction or DNA hybridization. The Th@SiO2 coupled nanobioprobes as both recognition probes and signal amplification indicators could mediate the ECL signals of Ru(bpy)3(2+)/tripropylamine (TPA) on the anodes of BPE array through faradaic reaction due to the charge neutrality of BPE. Thus, multiplex detection of cancer biomarkers (adenosine triphosphate (ATP), prostate-specific antigen (PSA), α-fetoprotein (AFP) and thrombin) is realized by forming specific sensing interfaces onto the cathodic poles of BPEs in different sensing channels and reported by the ECL images of the Ru(bpy)3(2+)/TPA system on the anodic poles of BPEs in detection channels. The results demonstrate that this visual ECL platform enables sensitive detection with excellent reproducibility, which may open a new door toward the development of simple, sensitive, cost-effective, and high throughput detection methods on biochips.