Assembly-line manipulation of droplets in microfluidic platform for fluorescence encoding and simultaneous multiplexed DNA detection

MRBLES 2.0: High-throughput generation of chemically functionalized spectrally and magnetically encoded hydrogel beads using a simple single-layer microfluidic device

The widespread adoption of bead-based multiplexed bioassays requires the ability to easily synthesize encoded microspheres and conjugate analytes of interest to their surface. Here, we present a simple method (MRBLEs 2.0) for the efficient high-throughput generation of microspheres with ratiometric barcode lanthanide encoding (MRBLEs) that bear functional groups for downstream surface bioconjugation. Bead production in MRBLEs 2.0 relies on the manual mixing of lanthanide/polymer mixtures (each of which comprises a unique spectral code) followed by droplet generation using single-layer, parallel flow-focusing devices and the off-chip batch polymerization of droplets into beads. To streamline downstream analyte coupling, MRBLEs 2.0 crosslinks copolymers bearing functional groups on the bead surface during bead generation. Using the MRBLEs 2.0 pipeline, we generate monodisperse MRBLEs containing 48 distinct well-resolved spectral codes with high throughput (>150,000/min and can be boosted to 450,000/min). We further demonstrate the efficient conjugation of oligonucleotides and entire proteins to carboxyl MRBLEs and of biotin to amino MRBLEs. Finally, we show that MRBLEs can also be magnetized via the simultaneous incorporation of magnetic nanoparticles with only a minor decrease in the potential code space. With the advantages of dramatically simplified device fabrication, elimination of the need for custom-made equipment, and the ability to produce spectrally and magnetically encoded beads with direct surface functionalization with high throughput, MRBLEs 2.0 can be directly applied by many labs towards a wide variety of downstream assays, from basic biology to diagnostics and other translational research.

A Thioflavin T-induced G-Quadruplex Fluorescent Biosensor for Target DNA Detection

The detection of disease-related DNA is of great significance for early and accurate diagnosis and therapy. In this work, we successfully achieved the sensitive detection of target DNA based on a thioflavin T (ThT)-induced G-quadruplex fluorescent biosensor. ThT, a water-soluble fluorescent dye, can induce G-rich sequences to form G-quadruplexes and obtain an obviously enhanced fluorescence. In this work, it was employed to construct a biosensor for the detection of HIV. When the target HIV existed, the hairpin DNA probes would be opened in succession and release the completely exposed G-rich sequence to combine with ThT. The simple and rapid biosensor performed satisfactory selectivity; it also exhibited sensitivity with a detection limit of 2.4 nM. With good performance in human serum, we believe that this optical biosensor has the potential to be applied to the practical detection of target DNA.

The synthesis of a smart streptavidin-functionalized poly(N-isopropylacrylamide) composite and its application in the separation and detection of virus nucleic acid

A new kind of polymeric material (PNIPAAm-co-SA) was prepared by conjugating a thermosensitive polymer, Poly (N-isopropylacrylamide) (PNIPAAm) with streptavidin (SA). This smart prepared composite displayed a controllable conformation change between an expanded and a collapsed form, below or above its lower critical solution temperature (LCST). Differential scanning calorimetry (DSC) analysis demonstrated that the PNIPAAm-co-SA bioconjugate showed the same LCST as the original synthetic polymer, PNIPAAm, which was also 32°C. Based on the specific interaction between SA and biotin, a higher capture efficiency of PNIPAAm-co-SA, which was almost 100% in PBS buffer solution and above 70% in serum was obtained, respectively. And the high affinity between PNIPAAm-co-SA and biotin was still maintained after three heating cycles. Subsequently, the variola virus (small pox, VV) oligonucleotide sequence was chosen as a model to demonstrate the sensitivity of the biosensor which was fabricated based on PNIPAAm-co-SA. The biosensor exhibited the ability to separate and enrich targets from complicated system with its phase transition ability, and high sensitivity toward VV-targets were achieved. Moreover, other types of targets such as proteins and cells, could be detected by changing the biotin-captures, which indicated the broad applicability of biosensors based on this smart polymer material.

Exonuclease III-based target recycling for ultrasensitive homogeneous monitoring of HIV DNA using Ag(+)-coordinated hairpin probe

A new homogeneous electrochemical sensing strategy based on exonuclease III-assisted target recycling amplification was utilized for simple, rapid and highly sensitive detection of human immunodeficiency virus (HIV) DNA on an immobilization-free Ag(I)-assisted hairpin DNA through the cytosine-Ag(+)-cytosine coordination chemistry. The assay involved target-induced strand-displacement reaction accompanying dissociation of the chelated Ag(+) in the hairpins and exonuclease III-triggered target recycling. Initially, the added target DNA hybridized with hairpin DNA to disrupt the Ag(I)-coordinated hairpin probe and releases the coordinated Ag(+) ion. Then, the newly formed DNA double-stranded DNA could be cleaved by exonuclease III, and released target HIV DNA, which retriggered the strand-displacement reaction with the hairpin for target recycling, thereby resulting in formation of numerous free Ag(+) ions in the detection cell. The released Ag(+) ions can be readily captured by the negatively charged electrode, and subsequent anodic-stripping voltammetric detection of the captured Ag(+) ions are conducted to form the anodic current for the production of the electronic signal within the applied potential. Under optimal conditions, the exonuclease III-based sensing system exhibited good electrochemical responses for the detection of HIV DNA at a concentration as low as 23 fM.

Hybridization-induced Ag(i) dissociation from an immobilization-free and label-free hairpin DNA: toward a novel electronic monitoring platform

A novel silver ion-assisted hairpin DNA through C–Ag⁺–C coordination chemistry was designed for homogeneous electronic monitoring of HIV DNA on a negatively charged electrode, based on hybridization-induced Ag⁺ dissociation from hairpin DNA.