Enhancing deoxyribonucleic acid (DNA) detection sensitivity through microconcentration on patterned fluorocarbon polymer surface

Self-Assembled Pico-Liter Droplet Microarray for Ultrasensitive Nucleic Acid Quantification

Nucleic acid detection and quantification technologies have made remarkable progress in recent years. Among existing platforms, hybridization-based assays have the advantages of being amplification free, low instrument cost, and high throughput, but are generally less sensitive compared to sequencing and PCR assays. To bridge this performance gap, we developed a quantitative physical model for the hybridization-based assay to guide the experimental design, which leads to a pico-liter droplet environment with drastically enhanced performance and detection limit several order above any current microarray platform. The pico-liter droplet hybridization platform is further coupled with the on-chip enrichment technique to yield ultrahigh sensitivity both in terms of target concentration and copy number. Our physical model, taking into account of molecular transport, electrostatic intermolecular interactions, reaction kinetics, suggests that reducing liquid height and optimizing target concentration will maximize the hybridization efficiency, and both conditions can be satisfied in a highly parallel, self-assembled pico-liter droplet microarray that produces a detection limit as low as 570 copies and 50 aM. The pico-liter droplet array device is realized with a micropatterned superhydrophobic black silicon surface that allows enrichment of nucleic acid samples by position-defined evaporation. With on-chip enrichment and oil encapsulated pico-liter droplet arrays, we have demonstrated a record high sensitivity, wide dynamic range (6 orders of magnitude), and marked reduction of hybridization time from >10 h to <5 min in a highly repeatable fashion, benefiting from the physics-driven design and nanofeatures of the device. The design principle and technology can contribute to biomedical sensing and point-of-care clinical applications such as pathogen detection and cancer diagnosis and prognosis.

Oil-encapsulated nanodroplet array for bio-molecular detection

Detection of low abundance biomolecules is challenging for biosensors that rely on surface chemical reactions. For surface reaction based biosensors, it require to take hours or even days for biomolecules of diffusivities in the order of 10(-10-11) m2/s to reach the surface of the sensors by Brownian motion. In addition, often times the repelling Coulomb interactions between the molecules and the probes further defer the binding process, leading to undesirably long detection time for applications such as point-of-care in vitro diagnosis. In this work, we designed an oil encapsulated nanodroplet array microchip utilizing evaporation for pre-concentration of the targets to greatly shorten the reaction time and enhance the detection sensitivity. The evaporation process of the droplets is facilitated by the superhydrophilic surface and resulting nanodroplets are encapsulated by oil drops to form stable reaction chamber. Using this method, desirable droplet volumes, concentrations of target molecules, and reaction conditions (salt concentrations, reaction temperature, etc.) in favour of fast and sensitive detection are obtained. A linear response over 2 orders of magnitude in target concentration was achieved at 10 fM for protein targets and 100 fM for miRNA mimic oligonucleotides.

Electrochemical detection of oligonucleotide by attaching redox probes onto its backbone

An approach was demonstrated to detect oligonucleotide by attaching redox probes onto its backbone. First, peptide nucleic acid (PNA) with a neutral backbone was immobilized onto a gold (Au) electrode surface as a capture. Second, when the PNA capture hybridized with a target oligonucleotide (a short DNA), an assembly of Au-PNA-DNA formed and phosphate groups were thus brought into the assembly from the DNA's backbone. The linker ion of Zr(4+) exhibits a strong coordination interaction with the phosphate group and the carboxylic group. The hybridized target DNA provides the phosphate group while a derivatized redox probe of ferrocene (Fc) carboxyl acid offers the carboxylic group. Therefore, the redox probe can be attached to the phosphate group by the linker to form an assembly of Au-PNA-DNA-Zr-Fc. Its redox process was studied and the detection conditions of oligonucleotide were optimized. A limit of detection of 1.0×10(-12) M or ∼2 attomol was reached.