Tandem Femto- and Nanomolar Analysis of Two Protein Biomarkers in Plasma on a Single Mixed Antibody Monolayer Surface Using Surface Plasmon Resonance

Simultaneous detection method for two cardiac disease protein biomarkers on a single chip modified with mixed aptamers using surface plasmon resonance

A simultaneous detection method for two cardiac disease protein biomarkers present in serum samples on a single planar gold chip using surface plasmon resonance (SPR) is described. The detection of N-terminal pro-brain natriuretic peptide (NT-proBNP) and tumor necrosis factor α (TNF-α), which are known as acute myocardial infarction (AMI) biomarkers, with predetermined clinically relevant concentrations was performed using mixed aptamers specific to each protein tethered on a single gold surface. After the binding of NT-proBNP and/or TNF-α to the mixed aptamers, an antibody specific to each target protein was injected to form a surface sandwich complex to improve selectivity. In order to adjust the dynamic ranges in the known clinically relevant concentration significantly different for NT-proBNP (0.13-0.24 nM) and TNF-α (0.5-3 pM), the surface density ratios of the corresponding pair of aptamer and antibody were first systematically determined, which were the 1:1 mixed aptamer chip with 40 nM anti-NT-proBNP and 100 nM anti-TNF-α. This allowed to establish the distinct dynamic ranges of 0.05-0.5 nM for NT-proBNP and 0.1-5 pM for TNF-α in a buffer, along with detection and quantification limits of 0.03 and 0.19 nM for NT-proBNP and 0.06 and 0.21 pM for TNF-α, respectively. The changes in refractive unit (RU) values observed when exposing both proteins at different concentrations alongside the corresponding fixed concentration of antibodies onto the 1:1 mixed aptamer chip were then correlated to the sum of RU values measured when using the injection of individual protein for evaluating each protein concentration. With a complete characterization of the simultaneous quantification of two protein concentrations in the buffer, the mixed aptamer chip was finally employed for direct measurements of NT-proBNP and TNF-α concentrations in undiluted serum samples from healthy controls and AMI patients. The results of simultaneous SPR measurements for the two proteins in the serum samples were further compared to the individual protein concentration results using an enzyme-linked immunosorbent assay.

Advances in the development paradigm of biosample-based biosensors for early ultrasensitive detection of alzheimer's disease

This review highlights current developments, challenges, and future directions for the use of invasive and noninvasive biosample-based small biosensors for early diagnosis of Alzheimer's disease (AD) with biomarkers to incite a conceptual idea from a broad number of readers in this field. We provide the most promising concept about biosensors on the basis of detection scale (from femto to micro) using invasive and noninvasive biosamples such as cerebrospinal fluid (CSF), blood, urine, sweat, and tear. It also summarizes sensor types and detailed analyzing techniques for ultrasensitive detection of multiple target biomarkers (i.e., amyloid beta (Aβ) peptide, tau protein, Acetylcholine (Ach), microRNA137, etc.) of AD in terms of detection ranges and limit of detections (LODs). As the most significant disadvantage of CSF and blood-based detection of AD is associated with the invasiveness of sample collection which limits future strategy with home-based early screening of AD, we extensively reviewed the future trend of new noninvasive detection techniques (such as optical screening and bio-imaging process). To overcome the limitation of non-invasive biosamples with low concentrations of AD biomarkers, current efforts to enhance the sensitivity of biosensors and discover new types of biomarkers using non-invasive body fluids are presented. We also introduced future trends facing an infection point in early diagnosis of AD with simultaneous emergence of addressable innovative technologies.

Recent advances in functionalization of plasmonic nanostructures for optical sensing

This review summarizes the progress that has been made in the use of nanostructured SPR-based chemical sensors and biosensors. Following an introduction into the field, a first large section covers principles of nanomaterial-based SPR sensing, mainly on methods using noble metal nanoparticles (spheres, cubes, triangular plates, etc.). The next section covers methods for functionalization of plasmonic nanostructures, with subsections on functionalization using (a) amino acids and proteins; (b) oligonucleotides, (c) organic polymers, and (d) organic compounds. Several tables are presented that give an overview on the wealth of methods and materials published. A concluding section summarizes the current status, addresses current challenges, and gives an outlook on potential future trends. This review is not intended to be a comprehensive compilation of the literature in the field but rather is a systematic overview of the state of the art in surface chemistry of plasmonic nanostructures. The ability of various ligands and receptors for functionalization of nanoparticles as well as their sensing capability is discussed.

Polyvalent Biotinylated Aptamer Scaffold for Rapid and Sensitive Detection of Tau Proteins

Biomimetic construction of artificial scaffolds has attracted increasing attention. However, the construction methods usually require redundant materials and procedures, which is inconvenient for further application. Herein, inspired by the polyvalent multifunctional structure in nature, we have designed a polyvalent biotinylated aptamer scaffold (PBAS) which can conduct analytical performance with high sensitivity and simplified procedures. To construct a PBAS, the aptamers are designed to hybridize with prepared linker probes to form polyvalent biotinylated scaffolds, which contain both multiple aptamers and signal labels. Therefore, multifunctional scaffolds can be constructed with high recognition and capture efficiency as well as significant signal amplification. Furthermore, the scaffold can be used for the assay of some disease marker proteins. By taking tau proteins as an example, the proposed aptasensor can exhibit excellent performance with a low detection limit of 153 pg mL^-1 and a short assay time of 50 min, which is much better than most of the previous methods. By assays of tau proteins in both serum and artificial cerebro spinal fluid, the PBAS-based aptasensor can work well. Therefore, the scaffold may be expected to be a powerful analytical tool which may have wide applications in the detection of a variety of analytes.

Femtomolar sensing of Alzheimer's tau proteins by water oxidation-coupled photoelectrochemical platform

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder. A key pathogenic event of AD is the formation of intracellular neurofibrillary tangles that are mainly composed of tau proteins. Here, we report on ultrasensitive detection of total tau (t-tau) proteins using an artificial electron donor-free, BiVO₄-based photoelectrochemical (PEC) analysis. The platform was constructed by incorporating molybdenum (Mo) dopant and iron oxyhydroxide (FeOOH) ad-layer into the BiVO₄ photoelectrode and employing a signal amplifier formed by horseradish peroxidase (HRP)-triggered oxidation of 3,3'-diaminobenzidine (DAB). Despite the absence of additional electron suppliers, the FeOOH/Mo:BiVO₄ conjugated with the Tau5 antibody produced strong current signals at 0 V (vs. Ag/AgCl, 3 M NaCl) under the illumination of a white light-emitting diode. The Mo extrinsic dopants increased the charge carrier density of BiVO₄-Tau5 by 1.57 times, and the FeOOH co-catalyst promoted the interfacial water oxidation reaction of Mo:BiVO₄-Tau5 by suppressing charge recombination. The introduction of HRP-labeled Tau46 capture antibodies to the FeOOH/Mo:BiVO₄-Tau5 platform produced insoluble precipitation on the transducer by accelerating the oxidation of DAB, which amplified the photocurrent signal of FeOOH/Mo:BiVO₄-Tau5 by 2.07-fold. Consequently, the water oxidation-coupled, FeOOH/Mo:BiVO₄-based PEC sensing platform accurately and selectively recognized t-tau proteins down to femtomolar concentrations; the limit of detection and limit of quantification were determined to be 1.59 fM and 4.11 fM, respectively.

A surface plasmon resonance biosensor in conjunction with a DNA aptamer-antibody bioreceptor pair for heterogeneous nuclear ribonucleoprotein A1 concentrations in colorectal cancer plasma solutions

A new DNA aptamer and antibody pair was incorporated into surface plasmon resonance (SPR) sensing platform to detect heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) in plasma at clinically relevant native concentrations for the diagnosis of colorectal cancer (CRC). SPR detection of hnRNP A1 was realized via formation of the surface sandwich complex of aptamer/hnRNP A1/anti-hnRNP A; the specific adsorption of hnRNP A1 onto a gold chip surface modified with a DNA aptamer followed by the adsorption of anti-hnRNP A1. Changes in the refractive unit (RU) with respect to the hnRNP A1 concentration in buffer solutions were monitored at a fixed anti-hnRNP A1 concentration of 90 nM, resulting in a dynamic range of 0.1-10 nM of hnRNP A1. The surface sandwich SPR biosensor was further applied to the direct analysis of undiluted human normal and pooled CRC patient plasma solutions. Our plasma analysis results were compared to those obtained with a commercial enzyme-linked immunosorbent assay kit.

Biosensors on the road to early diagnostic and surveillance of Alzheimer's disease

Alzheimer's disease is a debilitating and largely untreatable condition with subtle onset and slow progression over an extensive period of time, which culminate in increasing levels of disability. As Alzheimer's disease prevalence is expected to grow exponentially in the upcoming decades, there is an urgency to develop analytical technologies for the sensitive, reliable and cost-effective detection of Alzheimer's disease biomarkers. Biosensors are powerful analytical devices that translate events of biological recognition on physical or chemical transducers into electrical, thermal or optical signals. The high sensitivity and selectivity of biosensors associated with easy, rapid and low-cost determination of analytes have made this discipline one of the most intensively studied in the past decades. This review centers on recent advances, challenges and trends of Alzheimer's disease biosensing particularly in the effort to combine the unique properties of nanomaterials with biorecognition elements. In the last decade, impressive progresses have been made towards the development of biosensors, mainly electrochemical and optical, for detection of Alzheimer's disease biomarkers in the pico- and femto-molar range. Nonetheless, advances in multiplexed detection, robustness, stability and specificity are still necessary to ensure an accurate and differentiated diagnosis of this disease.

Chemical sensing platforms for detecting trace-level Alzheimer's core biomarkers

This review provides an overview of recent advances in optical and electrical detection of Alzheimer's disease biomarkers in clinically relevant fluids.

Advancements in SPR biosensing technology: An overview of recent trends in smart layers design, multiplexing concepts, continuous monitoring and in vivo sensing

Inspired by the rapid progress and existing limitations in surface plasmon resonance (SPR) biosensing technology, we have summarized the recent trends in the fields of both chip-SPR and fiber optic (FO)-SPR biosensors during the past five years, primarily regarding smart layers design, multiplexing, continuous monitoring and in vivo sensing. Versatile surface chemistries, biomaterials and nanomaterials have been utilized thus far to generate smart layers on SPR platforms and as such achieve oriented immobilization of bioreceptors, improved fouling resistance and sensitivity enhancement, collectively aiming to improve the biosensing performance. Furthermore, often driven by the desires for time- and cost-effective quantification of multiple targets in a single measurement, efforts have been made to implement multiplex bioassays on SPR platforms. While this aspect largely remains difficult to attain, numerous alternative strategies arose for obtaining parallel analysis of multiple analytes in one single device. Additionally, one of the upcoming challenges in this field will be to succeed in using SPR platforms for continuous measurements and in vivo sensing, and as such match up other biosensing platforms where these goals have been already conquered. Overall, this review will give insight into multiple possibilities that have become available over the years for boosting the performance of SPR biosensors. However, because combining them all into one optimal sensor is practically not feasible, the final application needs to be considered while designing an SPR biosensor, as this will determine the requirements of the bioassay and will thus help in selecting the essential elements from the recent progress made in SPR sensing.

Synchronous screening of multiplexed biomarkers of Alzheimer's disease by a length-encoded aerolysin nanopore-integrated triple-helix molecular switch

A label-free triple-helix molecular switch-mediated nanopore sensor is developed for the synchronous screening of biomarkers of Alzheimer's disease.