Microparticle-Based Detection of Viruses

Surveillance of viral pathogens in both point-of-care and clinical settings is imperative to preventing the widespread propagation of disease-undetected viral outbreaks can pose dire health risks on a large scale. Thus, portable, accessible, and reliable biosensors are necessary for proactive measures. Polymeric microparticles have recently gained popularity for their size, surface area, and versatility, which make them ideal biosensing tools. This review cataloged recent investigations on polymeric microparticle-based detection platforms across eight virus families. These microparticles were used as labels for detection (often with fluorescent microparticles) and for capturing viruses for isolation or purification (often with magnetic microparticles). We also categorized all methods by the characteristics, materials, conjugated receptors, and size of microparticles. Current approaches were compared, addressing strengths and weaknesses in the context of virus detection. In-depth analyses were conducted for each virus family, categorizing whether the polymeric microparticles were used as labels, for capturing, or both. We also summarized the types of receptors conjugated to polymeric microparticles for each virus family.

Surface Charge-Reversible Tubular Micromotors for Extraction of Nucleic Acids in Microsystems

Extraction of nucleic acids in microsystems is of significance for biomedical applications, but the current extraction methods generally require sophisticated microchannels and external equipment, hindering their practical applications. In this work, we have demonstrated a simple, versatile and efficient approach to extract nucleic acids in microsystems by developing cationic branched polyethyleneimine (PEI)-functionalized tubular micromotors. The as-developed tubular micromotors are fabricated by a two-step process combining the template-assisted electrodeposition and carbodiimide chemistry, and contain an inner catalytic Pt layer, a middle magnetic Ni layer and an outer cationic PEI layer. They exhibit autonomous bubble-propelled motion in aqueous hydrogen peroxide solutions, which can be guided by an external magnetic field, and the surface charges can be reversibly modulated by changing the pH value of the solution. Consequently, the as-developed tubular micromotors can selectively absorb nucleic acids from acidic solutions and desorb them into alkaline solutions, leading to the extraction of nucleic acids with high efficiency without external stirring. Furthermore, they can be operated in a microchannel chip without the aid of a pumping system. Our results indicate that this PEI-functionalized tubular micromotor platform provides a novel, simple and versatile microsystem nucleic acid extraction technology, holding considerable promise for important practical applications.

Tubular Micro/Nanomotors: Propulsion Mechanisms, Fabrication Techniques and Applications

Micro/nanomotors are self-propelled machines that can convert various energy sources into autonomous movement. With the great advances of nanotechnology, Micro/Nanomotors of various geometries have been designed and fabricated over the past few decades. Among them, the tubular Micro/Nanomotors have a unique morphology of hollow structures, which enable them to possess a strong driving force and easy surface functionalization. They are promising for environmental and biomedical applications, ranging from water remediation, sensing to active drug delivery and precise surgery. This article gives a comprehensive and clear review of tubular Micro/Nanomotors, including propulsion mechanisms, fabrication techniques and applications. In the end, we also put forward some realistic problems and speculate about corresponding methods to improve existing tubular Micro/Nanomotors.

Fluorometric detection of mutant DNA oligonucleotide based on toehold strand displacement-driving target recycling strategy and exonuclease III-assisted suppression

We describe here a fluorometric assay for sensitive detection of oligonucleotides, based on a target recycling amplification strategy driven by toehold-mediated strand displacement reaction and on exonuclease III (Exo Ш)-assisted fluorescence background suppression strategy. The network consists of a pair of partially complementary DNA hairpins (HP1 and HP2) with 3' overhang ends, between which the spontaneous hybridization is kinetically hindered by the stems. The target DNA is repeatedly used to trigger a recycling progress between the hairpins, generating numerous HP1-HP2 duplex complexes. Exo III was then employed to digest the double strand parts of the residual hairpins and the intermediate products. The fluorescent dye, SYBR Green I, binds to the double-strand DNA products and emits strong fluorescence to achieve sensitive detection of the target DNA with the detection limit of 5.34 pM. Moreover, this proposed strategy showed high discrimination efficiency towards target DNA against mismatched DNA and was successfully applied in the analysis of human serum sample.

Sensitive detection for coralyne and mercury ions based on homo-A/T DNA by exonuclease signal amplification

Based on specific homo-A/T DNA binding properties, a strategy for coralyne and mercury ions detection was realised by exonuclease-aided signal amplification. Coralyne could specifically bind homo-A DNA and protect it from the hydrolysis of exonuclease I. The coralyne-protected DNA was subsequently used as a trigger strand to hydrolyze DNA2 in exonuclease-aided signal amplification process. Thiazole orange was used to quantify the remainder DNA2. Under the optimal condition, the fluorescence intensity was linearly proportional to the concentration of coralyne in the range of 0.2-100 nM with a limit of detection (LOD) of 0.31 nM, which presented the lowest LOD for coralyne among all reported. With homo-T and Hg(2+) taking the place of homo-A DNA and coralyne, respectively, the system could also be used for Hg(2+) detection. The experiments in real samples also showed good results. This method was label-free, low-cost, easy-operating and highly repeatable for the detection of coralyne and mercury ions. It could also be extended to detect various analytes, such as other metal ions, proteins and small molecules by using appropriate aptamers.

Highly sensitive DNA detection using cascade amplification strategy based on hybridization chain reaction and enzyme-induced metallization

A novel highly sensitive colorimetric assay for DNA detection using cascade amplification strategy based on hybridization chain reaction and enzyme-induced metallization was established. The DNA modified superparamagnetic beads were demonstrated to capture and enrich the target DNA in the hybridization buffer or human plasma. The hybridization chain reaction and enzyme-induced silver metallization on the gold nanoparticles were used as cascade signal amplification for the detection of target DNA. The metalization of silver on the gold nanoparticles induced a significant color change from red to yellow until black depending on the concentration of the target DNA, which could be recognized by naked eyes. This method showed a good specificity for the target DNA detection, with the capabilty to discriminate single-base-pair mismatched DNA mutation (single nucleotide polymorphism). Meanwhile, this approach exhibited an excellent anti-interference capability with the convenience of the magentic seperation and washing, which enabled its usage in complex biological systems such as human blood plasma. As an added benefit, the utilization of hybridization chain reaction and enzyme-induced metallization improved detection sensitivity down to 10pM, which is about 100-fold lower than that of traditional unamplified homogeneous assays.

A graphene oxide and exonuclease-aided amplification immuno-sensor for antigen detection

We have developed a novel immuno-sensor applied to protein detection based on exonuclease III (Exo III)-induced signal amplification, multiplex binding of the biotin-streptavidin system and the fluorescence quenching ability of graphene oxide.

An ultrasensitive electrochemical method for detection of Ag(+) based on cyclic amplification of exonuclease III activity on cytosine-Ag(+)-cytosine

Ag(+) is known to bind very strongly with cytosine-cytosine (C-C) mismatches in DNA duplexes to form C-Ag(+)-C base pairs. Exonuclease III (Exo III) can catalyze the stepwise removal of mononucleotides of duplex DNA. In this work, we study Exo III activity on DNA hybrids containing C-Ag(+)-C base pairs. Our experiments show that Ag(+) ions could intentionally trigger the activity of Exo III towards a designed cytosine-rich DNA oligonucleotide (C-rich probe) by the conformational change of the probe. Our sensing strategy uses this conformation-dependent activity of Exo III, which is controlled through the cyclical shuffling of Ag(+) ions between the solid DNA hybrid and the solution phase. This interesting conversion has led to the development of an ultrasensitive detection platform for Ag(+) ions with a detection limit of 0.03 nM and a total assay time possible within minutes. This simple detection strategy could also be used for the detection of other metal ions which exhibit specific interactions with natural or synthetic bases.

Ultrasensitive detection of small molecule-protein interaction via terminal protection of small molecule linked DNA and Exo III-aided DNA recycling amplification

Terminal protection of small molecule linked DNA assays amplified by Exo III-aided DNA recycling is developed for the detection of streptavidin-biotin interaction, with a detection limit of 0.8 fM streptavidin in the "turn-on" state, indicating that the proposed method is an ultrasensitive platform for the detection of small molecule-protein interactions.

An ultrasensitive biosensor for DNA detection based on hybridization chain reaction coupled with the efficient quenching of a ruthenium complex to CdTe quantum dots

A highly sensitive and selective DNA biosensor based on hybridization chain reaction is described, which combines CdTe quantum dots (QDs) and a ruthenium complex. Based on the variation of fluorescence signals of the CdTe QDs, the target DNA is determined.

Multiplexed DNA detection with a composite molecular beacon based on guanine-quenching

We developed a multiplexed DNA detection method with a composite molecular beacon (MB) probe based on guanine-quenching by synchronous fluorescence analysis. It is demonstrated by two types of tumor-suppressor genes namely exon segments of p16 (T1) and p53 (T2) genes. The composite MB probe includes two loops and two stems, and two fluorophores of 6-carboxyfluorescein group (FAM) and tetramethyl-6-carboxyrhodamine (TAMRA) are connected to the two ends of molecular beacon. Every stem portion of MB include four continuous nucleotides with guanine (G) base as quencher, every loop portion is a probe sequence that is complementary to a corresponding target sequence. In the absence of target DNA, the composite MBs are in the stem-closed form, the fluorescence of FAM and TAMRA are quenched by G bases. At this time, the fluorescence signals of FAM and TAMRA are all very low. In the presence of target DNA, the MBs hybridize with the target DNA and form double-strands, FAM and TAMRA are separated from G bases, and the fluorescence of FAM and TAMRA recovers simultaneously. Thus, the simultaneous detection of two targets of DNA can be realized by measuring fluorescence signals of FAM and TAMRA, respectively. Under the optimum conditions, the fluorescence intensities of FAM and TAMRA all exhibit good linear dependence on their target DNA concentration in the range from 5 × 10(-11) to 5.5 × 10(-9) M. The detection limit of T1 is 4 × 10(-11) M (3σ), and that of T2 is 3 × 10(-11) M. This composite MB can be applied to detect the real sample, and can be applied to detect two aleatoric sequences of DNA. Compared with previously reported methods of detecting multiplexed target DNA with MBs, the proposed method has some advantages including easy synthesis of composite MB probes, low detection cost and shorter analytical time.