Protein functionalized titania particle as a nanocarrier in a multiple signal antibody amplification strategy for ultrasensitive chemiluminescent immunoassay

Active droplet-array microfluidics-based chemiluminescence immunoassay for point-of-care detection of procalcitonin

The application of conventional chemiluminescence immunoassay (CLIA) in resource-limited settings is limited due to the large apparatus footprint, cumbersome operation and maintenance process, and high consumption of reagents. To address this issue, we developed an active droplet-array (ADA) microfluidics-based CLIA system, which consists of a compact microchip analyzer and microfluidic chips with preloaded reagents. The microfluidic chip contains microslit-connected microchambers, in which all the required reagents were preloaded in water-in-oil droplets. The microfluidic chip analyzer can manipulate five microfluidic chips in parallel in a single run. By interacting the microchip with magnetic, thermal, optical mechanisms programmatically, the entire workflow of CLIA can be accomplished in an automated manner. With the proposed CLIA, the detection of procalcitonin (PCT) can be completed in 12 min, with a limit of detection (LOD) of 0.044 ng mL^-1 and a detection range from 0.044 to 100 ng mL^-1. We found a good linear correlation between the microfluidic CLIA and the conventional electrochemiluminescence immunoassay (R²=0.98).The microfluidic CLIA has significant advantages over the conventional ELISA in detection sensitivity, dynamic range, instrument size and turnaround time, and can provide more consistent and reliable results than the lateral flow immunoassays. The compact microfluidic system can perform automated and parallelized CLIA in a short turnaround time, and thus well suited to Point-of-Care detection of disease biomarkers.

Highly Sensitive Fluorescence-Linked Immunosorbent Assay for the Determination of Human IgG in Serum Using Quantum Dot Nanobeads and Magnetic Fe3O4 Nanospheres

The aim of this study is to establish a new method with high sensitivity, accuracy, and stability for the determination of human IgG and then expand it to analyze severe acute respiratory syndrome corona virus 2 (SARS-CoV-2)-specific IgM and IgG, which is of great significance for the screening and diagnosis of COVID-19. In this study, the magnetic Fe3O4 nanospheres coupled with mouse antihuman IgG (Ab1IgG) were used as an immune capture probe (Fe3O4@Ab1IgG) to capture and separate the target, and rabbit antihuman IgG (Ab2IgG) coupled with highly luminescent quantum dot nanobeads (QBs) as a fluorescence detection probe (QBs@Ab2IgG) was used to realize high sensitivity detection. After the formation of a sandwich immunocomplex, the fluorescence intensity of the precipitate after magnetic separation was measured at the excitation wavelength of 370 nm. Under optimal conditions, a wide linear range varying from 0.005 to 40 ng·mL-1 was obtained for the detection of human IgG with a lower limit of detection at 4 pg·mL-1 (S/N = 3). The recoveries of intra- and interassays were 90.0-101.9 and 96.0-106.6%, respectively, and the relative standard deviations were 6.3-10.2 and 2.6-10.5%, respectively. Furthermore, the proposed method was successfully demonstrated to detect human IgG in serum samples, and the detection results were not statistically different (P > 0.05) from commercial enzyme-linked immunosorbent assay kits. This method is sensitive, fast, and accurate, which could be expanded to detect the specific IgM and IgG antibodies against SARS-CoV-2.

Expanding the scope of chemiluminescence in bioanalysis with functional nanomaterials

Nanomaterial-enabled chemiluminescence (CL) detection has become a growing area of interest in recent years. We review the development of nanomaterial-based CL detection strategies and their applications in bioanalysis. Much progress has been achieved in the past decade, but most attempts still remain in the proof-of-concept stage. This review highlights recent advances in nanomaterials in CL detection and organizes them into three groups based on their role in detection: as a sensing platform, as a signal probe, and applications in homogeneous systems. Furthermore, we have discussed the critical challenges we are facing and future prospects of this field.

A novel method for sensitive, low-cost and portable detection of hepatitis B surface antigen using a personal glucose meter

Hepatitis B virus (HBV) infection is the major public health problem leading cause of death worldwide. The most important diagnostic marker for this infection is hepatitis B surface antigen (HBsAg). In this study, a novel, inexpensive, portable and sensitive ELISA method was designed and investigated for diagnosis of HBsAg based on the functionalized Fe₃O₄ and Al₂O₃ nanoparticles, with the strategy for detecting the concentration of glucose using a cheap and accessible personal glucose meter (PGM). The ELISA system was constructed using hepatitis B antibody against HBsAg immobilized on streptavidin coated magnetic iron oxide particles (S-Fe₃O₄) as the capture antibody (Ab₁). In addition, another hepatitis B antibody against different epitope of HBsAg (Ab₂) and glucoamylase both were immobilized on Al₂O₃ nanoparticles. After formation of the sandwich immune complex between Ab₁ and Ab₂ immobilized on S-Fe₃O₄ and Al₂O₃ NPs, respectively, through HBsAg, starch was converted into glucose using glucoamylase. Then, the glucose concentration was measured using PGM. The concentration of HBsAg was calculated based on the linear relation between the concentrations of HBsAg and glucose. Under optimal conditions, this assay showed detection limit values of 0.3 to 0.4 ng ml^-1 for "ay" and "ad" subtypes of HBsAg, respectively. The results indicate that the designed assay is comparable to the commercial kits in terms of sensitivity, on-site, specificity, cost, simplicity, portability and reproducibility. The presented method can be used in disadvantaged areas of the world and blood transfusion centers. To the best of our knowledge, this is the first report of using PGMs for HBSAg detection.

A new label-free strategy for a highly efficient chemiluminescence immunoassay

A new label-free chemiluminescence (CL) immunoassay method which is based on the co-immobilization of a capture antibody and horseradish peroxidase (HRP) on the Au nanoparticle–chitosan composite interface is proposed for the cheap, fast and convenient detection of proteins.

A simple and sensitive label-free fluorescent approach for protein detection based on a Perylene probe and aptamer

Highly sensitive detection of proteins is of great importance for effective clinical diagnosis and biomedical research. However, so far most detection methods rely on antibody-based immunoassays and are usually laborious and time-consuming with poor sensitivity. Here, we developed a simple and ultra-sensitive method to detect a biomarker protein-thrombin by taking advantage of the fluorescent probe Perylene tetracarboxylic acid diimide (PTCDI) derivatives and thrombin aptamer. The water-soluble dye PTCDI shows strong fluorescence in buffer solution for the existence of free dye monomer, but becomes weak after aggregation through self-assembly on nucleic acid aptamer. In the presence of thrombin, it specifically binds to thrombin aptamer which causes the conformational transition between aptamer and PTCDI and results in a significant fluorescence recovery. The results showed that as low as 40 pM of thrombin could be detected by this method. The high sensitivity of the developed sensing system mainly attributes to the ultra-sensitivity of the fluorescence intensity changes of PTCDI. With the specificity of aptamer, the assay exhibited high selectivity for thrombin against three other proteins (bovine serum albumin, lysozyme, mouse IgG) and 1% diluted fetal bovine serum. The detection method might be extended to sensitive detection of a variety of proteins for its advantages of isothermal conditions required, simple and rapid without multiple separation and washing steps.

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.