Colorimetric immunosensing via protein functionalized gold nanoparticle probe combined with atom transfer radical polymerization

Inside-Out Oriented Choline Phosphate-Based Biomimetic Magnetic Nanomaterials for Precise Recognition and Analysis of C-Reactive Protein

Phospholipid-based materials exhibit great application potential in the fields of chemistry, biology, and pharmaceutical sciences. In this study, an inside-out oriented choline phosphate molecule, 2-{2-(methacryloyloxy)ethyldimethylammonium}ethyl n-butyl phosphate (MBP), was proposed and verified as a novel ligand of C-reactive protein (CRP) to enrich the functionality of these materials. Compared with phosphorylcholine (PC)-CRP interactions, the binding between MBP and CRP was not affected by the reverse position of phosphate and choline groups and even found more abundant binding sites. Thus, high-density MBP-grafted biomimetic magnetic nanomaterials (MBP-MNPs) were fabricated by reversible addition-fragmentation chain transfer polymerization based on thiol-ene click chemistry. The novel materials exhibited multifunctional applications for CRP including purification and ultrasensitive detection. On the one hand, higher specificity, recovery (90%), purity (95%), and static binding capacity (198.14 mg/g) for CRP were achieved on the novel materials in comparison with traditional PC-based materials, and the enriched CRP from patient serum can maintain its structural integrity and bioactivity. On the other hand, the CRP detection method combining G-quadruplex and thioflavin T developed with MBP-MNPs showed a lower detection limit (10 pM) and wider linear range (0.1-50 nM) than most PC-functionalized analytical platforms. Therefore, the inside-out oriented choline phosphate can not only precisely recognize CRP but also be combined with biomimetic nanomaterials to provide high application potential.

Exploring Sensitive Label-Free Multiplex Analysis with Raman-Coded Microbeads and SERS-Coded Reporters

Suspension microsphere immunoassays are rapidly gaining attention in multiplex bioassays. Accurate detection of multiple analytes from a single measurement is critical in modern bioanalysis, which always requires complex encoding systems. In this study, a novel bioassay with Raman-coded antibody supports (polymer microbeads with different Raman signatures) and surface-enhanced Raman scattering (SERS)-coded nanotags (organic thiols on a gold nanoparticle surface with different SERS signatures) was developed as a model fluorescent, label-free, bead-based multiplex immunoassay system. The developed homogeneous immunoassays included two surface-functionalized monodisperse Raman-coded microbeads of polystyrene and poly(4-tert-butylstyrene) as the immune solid supports, and two epitope modified nanotags (self-assembled 4-mercaptobenzoic acid or 3-mercaptopropionic acid on gold nanoparticles) as the SERS-coded reporters. Such multiplex Raman/SERS-based microsphere immunoassays could selectively identify specific paratope–epitope interactions from one mixture sample solution under a single laser illumination, and thus hold great promise in future suspension multiplex analysis for diverse biomedical applications.

Application of nanoparticles in cancer therapy with an emphasis on cell cycle

Owing to their unique characteristics, nanoparticles (NPs) could be incorporated into valuable therapeutic modalities for different diseases; however, there are many concerns about risk factors in human applications. NPs carry therapeutic chemicals that could improve the outcome of cancer therapies. Nowadays, NPs are being recognized as important and strategic agents in treatment of several disorders due to their unique properties in targeting malignant cells in tumor sites. Numerous investigations have shown that the majority of chemotherapeutic agents can be modified through entrapment in submicron colloidal systems. Still, there are problems and limitations in application of NPs in cancer therapy. The aim of the present study is to focus on potential NPs usage in cancer treatment with an emphasis on the cell cycle of malignant cells.

A sensitive immunosensor based on FRET between gold nanoparticles and InP/ZnS quantum dots for arginine kinase detection

Arginine kinase (AK) is one of the most important allergens in shrimp products. Herein, a novel immunoassay for quantitation of AK was developed using the antibody modified gold nanoparticle (AuNP) and quantum dot (QD). When the first antibody modified AuNP (AuNP-Ab1) was bridged by AK with the secondary antibody modified QD (QD-Ab2), fluorescence resonance energy transfer (FRET) would occur between the AuNP and QD, which led to a decrease in fluorescent signals. The decrease in fluorescence intensity was found to correlate linearly with the log of AK concentration in the range of 1.0 × 10^-6-1.0 × 10^-3 mg/mL (R² = 0.9909) and the detection limit was 0.11 ng/mL. The immunoassay was further proved to have encouraging specificity, precision and accuracy. Compared with existing methods, this study provided a promising approach to develop a highly sensitive and selective detection method for AK in shrimp related food samples.

Radical polymerization reactions for amplified biodetection signals

This review summarizes various radical polymerization chemistries for amplifying biodetection signals and compares them from the practical point of view.

Investigating Colorimetric Protein Array Assay Schemes for Detection of Recurrence of Bladder Cancer

A colorimetric microarray for the multiplexed detection of recurrence of bladder cancer including protein markers interleukin-8 (IL8), decorin (DCN), and vascular endothelial growth factor (VEGF) was established to enable easy and cheap read-out by a simple office scanner paving the way for quick therapy monitoring at doctors' offices. The chip is based on the principle of a sandwich immunoassay and was optimized prior to multiplexing using IL8 as a model marker. Six different colorimetric assay formats were evaluated using a detection antibody (dAB) labeled with (I) gold (Au) nanoparticles (NPs), (II) carbon NPs, (III) oxidized carbon NPs, and a biotinylated dAB in combination with (IV) neutravidin-carbon, (V) streptavidin (strp)-gold, and (VI) strp-horseradish peroxidase (HRP). Assay Format (III) worked best for NP-based detection and showed a low background while the enzymatic approach, using 3,3',5,5'-tetramethylbenzidine (TMB) substrate, led to the most intense signals with good reproducibility. Both assay formats showed consistent spot morphology as well as detection limits lower than 15 ng/L IL8 and were thus applied for the multiplexed detection of IL8, DCN, and VEGF in synthetic urine. Colorimetric detection in urine (1:3) yields reaction signals and measurement ranges well comparable with detection in the assay buffer, as well as excellent data reproducibility as indicated by the coefficient of variation (CV 5-9%).

A high-resolution colorimetric immunoassay platform realized by coupling enzymatic multicolor generation with smartphone readout

A high-resolution colorimetric immunoassay platform is developed based on dual enzyme-catalyzed multicolor generation and smartphone-assisted signal readout.

Exploiting pH-Regulated Dimer-Tetramer Transformation of Concanavalin A to Develop Colorimetric Biosensing of Bacteria

Gold nanoparticles (AuNPs) aggregation-based colorimetric biosensing remains a challenge for bacteria due to their large size. Here we propose a novel colorimetric biosensor for rapid detection of Escherichia coli O157:H7 (E. coli O157:H7) in milk samples based on pH-regulated transformation of dimer/tetramer of Concanavalin A (Con A) and the Con A-glycosyl recognition. Briefly, antibody-modified magnetic nanoparticles was used to capture and concentrate E. coli O157:H7 and then to label with Con A; pH adjusted to 5 was then applied to dissociate Con A tetramer to release dimer, which was collected and re-formed tetramer at pH of 7 to cause the aggregation of dextran-modified AuNPs. The interesting pH-dependent conformation-transformation behavior of Con A innovated the design of the release from the bacteria surface and then the reconstruction of Con A. Therefore, we realized the sensitive colorimetric biosensing of bacteria, which are much larger than AuNPs that is generally not suitable for this kind of method. The proposed biosensor exhibited a limit of detection down to 41 CFU/mL, short assay time (~95 min) and satisfactory specificity. The biosensor also worked well for the detection in milk sample, and may provide a universal concept for the design of colorimetric biosensors for bacteria and virus.

Colorimetric detection based on localised surface plasmon resonance of gold nanoparticles: Merits, inherent shortcomings and future prospects

Localised surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) has been exploited for two decades in analytical science and has proven to be a powerful tool for the detection of various kinds of substances including small molecules, ions, macro biomolecules and microbes. Detection can be performed by visual colour change observations, photometry or resonance light scattering. A wide range of applications have been studied in the areas of environmental, pharmaceutical and biological analysis and clinical diagnosis. In this article, some fundamental aspects and important applications involving LSPR of AuNPs are reviewed. Several inherent shortcomings of these techniques and possible strategies to circumvent them are discussed.

An ultrasensitive label-free electrochemical immunosensor based on signal amplification strategy of multifunctional magnetic graphene loaded with cadmium ions

Herein, a novel and ultrasensitive label-free electrochemical immunosensor was proposed for quantitative detection of human Immunoglobulin G (IgG). The amino functionalized magnetic graphenes nanocomposites (NH₂-GS-Fe₃O₄) were prepared to bond gold and silver core-shell nanoparticles (Au@Ag NPs) by constructing stable Au-N and Ag-N bond between Au@Ag NPs and -NH₂. Subsequently, the Au@Ag/GS-Fe₃O₄ was applied to absorb cadmium ion (Cd²⁺) due to the large surface area, high conductivity and exceptional adsorption capability. The functional nanocomposites of gold and silver core-shell magnetic graphene loaded with cadmium ion (Au@Ag/GS-Fe₃O₄/Cd²⁺) can not only increase the electrocatalytic activity towards hydrogen peroxide (H₂O₂) but also improve the effective immobilization of antibodies because of synergistic effect presented in Au@Ag/GS-Fe₃O₄/Cd²⁺, which greatly extended the scope of detection. Under the optimal conditions, the proposed immunosensor was used for the detection of IgG with good linear relation in the range from 5 fg/mL to 50 ng/mL with a low detection limit of 2 fg/mL (S/N = 3). Furthermore, the proposed immunosensor showed high sensitivity, special selectivity and long-term stability, which had promising application in bioassay analysis.

Preparation of Au-polydopamine functionalized carbon encapsulated Fe₃O₄ magnetic nanocomposites and their application for ultrasensitive detection of carcino-embryonic antigen

A novel carbon encapsulated Fe3O4 nanoparticles embedded in two-dimensional (2D) porous graphitic carbon nanocomposites (Fe3O4@C@PGC nanocomposites) were synthesized by situ synthesis strategy, which provided a sensor platform owing to a large aspect ratio and porous structure. Polydopamine (PDA) were modified on the surface of Fe3O4@C@PGC nanocomposites through self-polymerization of dopamine, acting as both the reductant and template for one-step synthesis of gold nanoparticles. The prepared Au/PDA/Fe3O4@C@PGC nanocomposites show ferromagnetic features, extremely excellent electron transfer, large specific surface area and excellent dispersing property. These are conducive to the electrochemical signal output and the immobilization of antibody. In this work, a highly label-free sensitive magnetic immunosensor was developed based on Au/PDA/Fe3O4@C@PGC nanocomposites for the detection of carcino-embryonic antigen (CEA). The magnetic glassy carbon electrode was used to fix the Au/PDA/Fe3O4@C@PGC nanocomposites with the help of magnetic force. Under the optimal conditions, the immunosensor exhibited a wide linear range (0.001 ng/mL-20.0 ng/mL), a low detection limit (0.33 pg/mL), good reproducibility, selectivity and acceptable stability. The proposed sensing strategy may provide a potential application in the detection of other cancer biomarkers.

Using photo-initiated polymerization reactions to detect molecular recognition

Radical polymerization reactions initiated by light can be used to provide signal amplification in molecular binding assays.

Copper-doped titanium dioxide nanoparticles as dual-functional labels for fabrication of electrochemical immunosensors

Constructions of versatile electroactive labels are key issues in the development of electrochemical immunosensors. In this study, copper-doped titanium dioxide nanoparticle (Cu@TiO2) was synthesized and used as labels for fabrication of sandwich-type electrochemical immunosensors on glassy carbon electrode (GCE). Due to the presence of copper ions, Cu@TiO2 shows a strong response current when coupled to an electrode. The prepared nanocomposite also shows high electrocatalytic activity towards reduction of hydrogen peroxide (H2O2). The dual functionality of Cu@TiO2 enables the fabrication of immunosensor using different detection modes, that is, square wave voltammetry (SWV) or chronoamperometry (CA). While Cu@TiO2 was used as labels of secondary antibodies (Ab2), carboxyl functionalized graphene oxide (CFGO) was used as electrode materials to immobilize primary antibodies (Ab1). Using human immunoglobulin G (IgG) as a model analyte, the immunosensor shows high sensitivity, acceptable stability and good reproducibility for both detection modes. Under optimal conditions, a linear range from 0.1 pg/mL to 100 ng/mL with a detection limit of 0.052 pg/mL was obtained for SWV analysis. For CA analysis, a wider linear range from 0.01 pg/mL to 100 ng/mL and a lower detection limit of 0.0043 pg/mL were obtained. The proposed metal ion-based enzyme-free and noble metal-free immunosensor may have promising applications in clinical diagnoses and many other fields.

Electrochemiluminescence resonance energy transfer between graphene quantum dots and gold nanoparticles for DNA damage detection

Electrochemiluminescence resonance energy transfer between graphene quantum dots (GQDs) and Au nanoparticles results in the electrochemiluminescence signal of the GQDs being quenched or recovering.

GOLD NANOPARTICLES-BASED BIOSENSORS FOR BIOMEDICAL APPLICATION

Gold nanoparticles are the most extensively studied nanomaterials for biomedical application due to their unique properties, such as rapid and simple synthesis, large surface area, strong adsorption ability and facile conjugation to various biomolecules. The remarkable photophysical properties of gold nanoparticles have provided plenty of opportunities for the preparation of gold nanoparticles-based optical biosensors, while the excellent biocompatibility, conductivity, catalytic properties and large surface-to-volume ratio have facilitated the application of gold nanoparticles in the construction of electrochemical biosensors. In this review, we mainly detail the gold nanoparticles-based optical and electrochemical biosensors for biomedical application in the recent two years, which have exhibited greatly enhanced analytical performances in the detection of DNA, proteins and some important small molecules.

Integrated tyramide and polymerization-assisted signal amplification for a highly-sensitive immunoassay

A novel strategy for ultrasensitive detection of model protein based on the integration of tyramide signal amplification (TSA) and polymerization-assisted signal amplification was proposed. The surface-initiated atom transfer radical polymerization (SI-ATRP) of glycidyl methacrylate (GMA) was triggered by the initiator-coupled protein immobilized on the electrode surface through sandwiched immunoreactions. Growth of long chain polymeric materials provided numerous epoxy groups for subsequent coupling of horseradish peroxidase (HRP), which in turn significantly increased the loading of quantum dots (QDs) labeled tyramide in the presence of hydrogen peroxide. As a result, electrochemiluminescence (ECL) and square-wave voltammetric (SWV) measurements showed 9.4- and 10.5-fold increase in detection signal in comparison with the unamplified method, respectively. To demonstrate the feasibility of this approach, human immunoglobulin G antigen (IgG) as a model target protein was employed and the detection limits were 0.73 and 0.09 pg mL(-1) for ECL and SWV, respectively. The results showed that sensitivity of the presented immunoassay significantly increased by one-order of magnitude and offered great application promises in providing a sensitive, specific, and potent method for biological detection.

Target-triggered polymerization for biosensing

Because of the potential applications of biosensors in clinical diagnosis, biomedical research, environmental analysis, and food quality control, researchers are very interested in developing sensitive, selective, rapid, reliable, and low-cost versions of these devices. A classic biosensor directly transduces ligand-target binding events into a measurable physical readout. Because of the limited detection sensitivity and selectivity in earlier biosensors, researchers have developed a number of sensing/signal amplification strategies. Through the use of nanostructured or long chain polymeric materials to increase the upload of signal tags for amplification of the signal readout associated with the ligand-target binding events, researchers have achieved high sensitivity and exceptional selectivity. Very recently, target-triggered polymerization-assisted signal amplification strategies have been exploited as a new biosensing mechanism with many attractive features. This strategy couples a small initiator molecule to the DNA/protein detection probe prior to DNA hybridization or DNA/protein and protein/protein binding events. After ligand-target binding, the in-situ polymerization reaction is triggered. As a result, tens to hundreds of small monomer signal reporter molecules assemble into long chain polymers at the location where the initiator molecule was attached. The resulting polymer materials changed the optical and electrochemical properties at this location, which make the signal easily distinguishable from the background. The assay time ranged from minutes to hours and was determined by the degree of amplification needed. In this Account, we summarize a series of electrochemical and optical biosensors that employ target-triggered polymerization. We focus on the use of atom transfer radical polymerization (ATRP), as well as activator generated electron transfer for atom transfer radical polymerization (AGET ATRP) for in-situ formation of polymer materials for optically or electrochemically transducing DNA hybridization and protein-target binding. ATRP and AGET ATRP can tolerate a wide range of functional monomers. They also allow for the preparation of well-controlled polymers with narrow molecular weight distribution, which was predetermined by the concentration ratio of the consumed monomer to the introduced initiator. Because the reaction initiator can be attached to a variety of detection probes through well-established cross-linking reactions, this technique could be expanded as a universal strategy for the sensitive detection of DNA and proteins. We see enormous potential for this new sensing technology in the development of portable DNA/protein sensors for point-of-need applications.