Ultrasensitive quantitation of MicroRNAs via magnetic beads-based chemiluminesent assay

Fabrication of functional interface on magnetic beads via various amino acids and their application in chemiluminescent immunoassay as carrier

Magnetic polymer microspheres with superparamagnetism, high specificity, and monodispersity play a crucial role in the field of in vitro diagnostics. However, the surface modification process of magnetic beads is often complex, and it remains a significant challenge to prepare high-performance magnetic beads easily. To overcome these drawbacks, herein we fabricated functional interface on magnetic bead with the various amino acid via the ring-opening reaction of amino acids with epoxy groups, with attempt to produce carboxylated magnetic beads (MPS-GA) in a convenient way. Results indicate that when compared to other amino acids, the phenylalanine magnetic beads (MPS-GA1) developed in this study exhibit strong adsorption for mouse immunoglobulin (IgG), streptavidin (SA), and protamine (PA), with an IgG adsorption capacity of 53.5 μg/mg and a coupling capacity of 52.5 μg/mg. It is found that electrostatic forces and hydrophobic interactions are key factors influencing biomolecular interactions. Additionally, these magnetic beads can generate strong chemiluminescent signals, significantly reducing background levels by up to 99.7 %. Therefore, the magnetic beads proposed in this paper can serve as carriers for chemiluminescent immunoassay (CLIA), providing new insights into the synthesis of high-quality magnetic bead.

M13 Bacteriophage-Assisted Recognition and Signal Spatiotemporal Separation Enabling Ultrasensitive Light Scattering Immunoassay

The demand for the ultrasensitive and rapid quantitative analysis of trace target analytes has become increasingly urgent. However, the sensitivity of traditional immunoassay-based detection methods is limited due to the contradiction between molecular recognition and signal amplification caused by the size effect of nanoprobes. To address this dilemma, we describe versatile M13 phage-assisted immunorecognition and signal transduction spatiotemporal separation that enable ultrasensitive light-scattering immunoassay systems for the quantitative detection of low-abundance target analytes. The newly developed immunoassay strategy combines the M13 phage-assisted light scattering signal fluctuations of gold nanoparticles (AuNPs) with gold in situ growth (GISG) technology. Given the synergy of M13 phage-mediated leverage effect and GISG-amplified light scattering signal modulation, the practical detection capability of this strategy can achieve the ultrasensitive and rapid quantification of ochratoxin A and alpha-fetoprotein in real samples at the subfemtomolar level within 50 min, displaying about 4 orders of magnitude enhancement in sensitivity compared with traditional phage-based ELISA. To further improve the sensitivity of our immunoassay, the biotin-streptavidin amplification scheme is implemented to detect severe acute respiratory syndrome coronavirus 2 spike protein down to the attomolar range. Overall, this study offers a direction for ultrasensitive quantitative detection of target analytes by the synergistic combination of M13 phage-mediated leverage effect and GISG-amplified light scattering signal modulation.

Real-time multiple signal amplification self-powered biosensing platform for ultrasensitive detection of MicroRNA

A real-time self-powered biosensor is designed for ultrasensitive detection of microRNA-21 based on electrochemical energy device capacitor and target-induced recycling double amplification strategy, which greatly improves the output signal by converting a small number of targets into two glucose oxidase labeled output strand DNAs, and the squeezed-out output strand is recycled by the cathode to fix more signal [Ru(NH₃)₆]³⁺ to further improve the detection signal. A digital multimeter (DMM) is connected to computer for real-time displaying the output signal of the self-powered biosensing system, which improves the accuracy of the sensing platform. The sensitivity of the proposed biosensor is 116.15 μA/pM for target microRNA-21, which is 32.26 times higher than that of pure EBFC (3.6 μA/pM). The target concentration is proportional to the open-circuit voltage value in a wide linear range of 0.1-10000 fM with a low detection limit of 0.04 fM (S/N = 3). The method shows high sensitivity and excellent selectivity, and can be applied to detect tumor marker microRNA-21 in biological matrix.

Recent progress of microfluidic chips in immunoassay

Microfluidic chip technology is a technology platform that integrates basic operation units such as processing, separation, reaction and detection into microchannel chip to realize low consumption, fast and efficient analysis of samples. It has the characteristics of small volume need of samples and reagents, fast analysis, low cost, automation, portability, high throughout, and good compatibility with other techniques. In this review, the concept, preparation materials and fabrication technology of microfluidic chip are described. The applications of microfluidic chip in immunoassay, including fluorescent, chemiluminescent, surface-enhanced Raman spectroscopy (SERS), and electrochemical immunoassay are reviewed. Look into the future, the development of microfluidic chips lies in point-of-care testing and high throughput equipment, and there are still some challenges in the design and the integration of microfluidic chips, as well as the analysis of actual sample by microfluidic chips.

Circulating Abnormal Extracellular Vesicles: Their Mechanism for Crossing Blood-Brain Barrier, Effects on Central Nervous System and Detection Methods

Central nervous system (CNS) diseases are difficult to treat and harmful. Many CNS diseases are secondary to peripheral diseases, such as tumor brain metastases (BMS), viral infections and inflammation of the brain, and their pathogenic factors travel through the circulatory system to the brain, eventually leading to lesions. Extracellular vesicles (EVs) play an important role in this process. Recent studies have shown that, extracellular EVs can effectively cross the blood- brain barrier (BBB) through endocytosis and they transmit molecular signals in cell-to-cell communication. Abnormal EVs produced in the lesion portion transport pathogenic factors, including miRNAs, proteins, and virions into the CNS. These pathogenic factors participate in cellular pathways to interfere with homeostasis or are themselves pathogens that directly damage CNS. In addition, different or specific pathological molecules in EVs are potential disease markers. We herein reviewed pathways through which the abnormal EVs cross BBB and adverse effects of abnormal exosomes. We also and summarized their existing detection techniques, so as to provide basis for prevention and early diagnosis of secondary diseases.

Aptasensors for pesticide detection

Pesticide contamination has become one of the most serious problems of public health in the world, due to their wide application in agriculture industry to guarantee the crop yield and quality. The detection of pesticide residues plays an important role in food safety management and environment protection. However, the conventional detection methodologies cannot realize highly sensitive, selective and on-site detection, which limits their applications. Aptamers are short single-stranded oligonucleotides (RNA or DNA) selected by SELEX method, which can selectively bind to their targets with high affinity. Compared with the commonly used antibodies or enzymes in designing biosensors, aptamers exhibit better stability, low molecular weight, easy modification and low cost, and were regarded as excellent candidates for developing aptasensors for pesticide detection. In this review, application of aptamers for pesticide detection was reviewed. Firstly, aptamers specifically bind to various pesticides were first summarized. Secondly, the progresses and highlights of developing aptasensors for highly-sensitive and selective detection of pesticide residues were systematically provided. Finally, the present challenges and future perspectives for developing novel highly-effective aptasensor for the detection of pesticide residues were discussed.

An Allosteric-Probe for Detection of Alkaline Phosphatase Activity and Its Application in Immunoassay

A fluorescence strategy for alkaline phosphatase (ALP) assay in complicated samples with high sensitivity and strong stability is developed based on an allosteric probe (AP). This probe consists of two DNA strands, a streptavidin (SA) aptamer labeled by fluorophore and its totally complementary DNA (cDNA) with a phosphate group on the 5′ end. Upon ALP introduction, the phosphate group on the cDNA is hydrolyzed, leaving the unhydrolyzed cDNA sequence for lambda exonuclease (λ exo) digestion and releasing SA aptamer for binding to SA beads, which results in fluorescence enhancement of SA beads that can be detected by flow cytometry or microscopy. We have achieved a detection limit of 0.012 U/mL with a detection range of 0.02~0.15 U/mL in buffer and human serum. These figures of merit are better than or comparable to those of other methods. Because the fluorescence signal is localized on the beads, they can be separated to remove fluorescence background from complicated biological systems. Notably, the new strategy not only applies to ALP detection with simple design, easy operation, high sensitivity, and good compatibility in complex solution, but also can be utilized in ALP-linked immunosorbent assays for the detection of a wide range of targets.