Rapid sub-attomole microRNA detection on a portable microfluidic chip

Portable point-of-care diagnostic devices: an updated review

The global pandemic caused by the SARS-CoV-2 (COVID) virus indiscriminately impacted people worldwide with unquantifiable and severe impacts on all aspects of our lives, regardless of socioeconomic status. The pandemic brought to light the very real possibility of pathogens changing and shaping the way we live, and our lack of preparedness to deal with viral/bacterial outbreaks. Importantly, the quick detection of pathogens can help prevent and control the spread of disease, making the importance of diagnostic techniques undeniable. Point-of-care diagnostics started as a supplement to standard lab-based diagnostics, and are gradually becoming mainstream. Because of this, and their importance in detecting pathogens (especially in the developing world), their development has accelerated at an unprecedented rate. In this review, we highlight some important and recent examples of point-of-care diagnostics for detecting nucleic acids, proteins, bacteria, and other biomarkers, with the intent of making apparent their positive impact on society and human health.

Ready-to-use nanopore platform for the detection of any DNA/RNA oligo at attomole range using an Osmium tagged complementary probe

Nanopores can serve as single molecule sensors. We exploited the MinION, a portable nanopore device from Oxford Nanopore Technologies, and repurposed it to detect any DNA/RNA oligo (target) in a complex mixture by conducting voltage-driven ion-channel measurements. The detection and quantitation of the target is enabled by the use of a unique complementary probe. Using a validated labeling technology, probes are tagged with a bulky Osmium tag (Osmium tetroxide 2,2′-bipyridine), in a way that preserves strong hybridization between probe and target. Intact oligos traverse the MinION’s nanopore relatively quickly compared to the device’s acquisition rate, and exhibit count of events comparable to the baseline. Counts are reported by a publicly available software, OsBp_detect. Due to the presence of the bulky Osmium tag, probes traverse more slowly, produce multiple counts over the baseline, and are even detected at single digit attomole (amole) range. In the presence of the target the probe is “silenced”. Silencing is attributed to a 1:1 double stranded (ds) complex that does not fit and cannot traverse this nanopore. This ready-to-use platform can be tailored as a diagnostic test to meet the requirements for point-of-care cell-free tumor DNA (ctDNA) and microRNA (miRNA) detection and quantitation in body fluids.

Extracellular microRNAs in blood differentiate between ischaemic and haemorrhagic stroke subtypes

Rapid identification of patients suffering from cerebral ischaemia, while excluding intracerebral haemorrhage, can assist with patient triage and expand patient access to chemical and mechanical revascularization. We sought to identify blood-based, extracellular microRNAs 15 (ex-miRNAs) derived from extracellular vesicles associated with major stroke subtypes using clinical samples from subjects with spontaneous intraparenchymal haemorrhage (IPH), aneurysmal subarachnoid haemorrhage (SAH) and ischaemic stroke due to cerebral vessel occlusion. We collected blood from patients presenting with IPH (n = 19), SAH (n = 17) and ischaemic stroke (n = 21). We isolated extracellular vesicles from plasma, extracted RNA cargo, 20 sequenced the small RNAs and performed bioinformatic analyses to identify ex-miRNA biomarkers predictive of the stroke subtypes. Sixty-seven miRNAs were significantly variant across the stroke subtypes. A subset of exmiRNAs differed between haemorrhagic and ischaemic strokes, and LASSO analysis could distinguish SAH from the other subtypes with an accuracy of 0.972 ± 0.002. Further analyses predicted 25 miRNA classifiers that stratify IPH from ischaemic stroke with an accuracy of 0.811 ± 0.004 and distinguish haemorrhagic from ischaemic stroke with an accuracy of 0.813 ± 0.003. Blood-based, ex-miRNAs have predictive value, and could be capable of distinguishing between major stroke subtypes with refinement and validation. Such a biomarker could one day aid in the triage of patients to expand the pool eligible for effective treatment.

Sensitivity Enhancement of MicroRNA Detection Using a Power-free Microfluidic Chip

We present a microRNA (miRNA) detection method that achieves enhanced sensitivity by means of a power-free microfluidic chip without the requirement of an external power source. The miRNA detection is completed by sandwich hybridization between probe DNAs and target miRNA with small sample volume (0.5 μL) within 20 min. Fluorescence signals after hybridization were amplified by laminar flow-assisted dendritic amplification (LFDA) using fluorescein isothiocyanate (FITC)-labeled streptavidin (F-SA) and biotinylated anti-streptavidin (B-anti-SA) as amplification reagents. To enhance the sensitivity of on-chip miRNA detection, the hybridization buffer solution was newly optimized with three main components-sodium dodecyl sulfate (SDS), formamide and dextran sulfate-that are known to strongly influence hybridization. An on-chip miRNA detection test in the newly optimized hybridization buffer (0.2% SDS, 5% formamide and 1% dextran sulfate) revealed dramatic increases in both the LFDA signal in the sample channel and the signal-to-background ratio (S/B ratio). Moreover, the LFDA signals in a blank reference channel remained low due to the suppression of non-specific bindings and hybridizations. By changing the hybridization buffer, we obtained an improved limit of detection (LOD) that was 0.045 pM (miRNA-196a) and 0.45 pM (miRNA-331), which are around 30- and 10-fold better than that of when control hybridization buffer was used. The improved performance of our miRNA detection system with short running time and high sensitivity could contribute to future research, including point-of-care diagnostic systems.

Plasmofluidics for Biosensing and Medical Diagnostics

Plasmofluidics, an extension of optofluidics into the nanoscale regime, merges plasmonics and micro-/nanofluidics for highly integrated and multifunctional lab on a chip. In this chapter, we focus on the applications of plasmofluidics in the versatile manipulation and sensing of biological cell, organelles, molecules, and nanoparticles, which underpin advanced biomedical diagnostics.

A robust, portable and backflow-free micromixing device based on both capillary- and vacuum-driven flows

A robust, portable and backflow-free micromixing device using capillary-driven bypassing and syringe-assisted vacuum-driven pumping shows great promise for a variety of blood typing assays, agglutination-based assays and point-of-care or lab-on-a-chip testing applications.

MicroRNA-122 can be measured in capillary blood which facilitates point-of-care testing for drug-induced liver injury

AIMS

Liver-enriched microRNA-122 (miR-122) is a novel circulating biomarker for drug-induced liver injury (DILI). To date, miR-122 has been measured in serum or plasma venous samples. If miR-122 could be measured in capillary blood obtained from a finger prick it would facilitate point-of-care testing, such as in resource-limited settings that have a high burden of DILI.

METHODS

In this study, in healthy subjects, miR-122 was measured by polymerase chain reaction in three capillary blood drops taken from different fingers and in venous blood and plasma (n = 20). miR-122 was also measured in capillary blood obtained from patients with DILI (n = 8).

RESULTS

Circulating miR-122 could be readily measured in a capillary blood drop in healthy volunteers with a median (interquartile range) cycle threshold (Ct) of 32.6 (31.1-34.2). The coefficient of variation for intraindividual variability across replicate blood drops was 49.9%. Capillary miR-122 faithfully reflected the concentration in venous blood and plasma (Pearson R = 0.89, P < 0.0001; 0.88, P < 0.0001, respectively). miR-122 was 86-fold higher in DILI patients [median value 1.0 × 10⁸ (interquartile range 1.89 × 10⁷ -3.04 × 10⁹ ) copies/blood drop] compared to healthy subjects [1.85 × 10⁶ (4.92 × 10⁵ -5.88 × 10⁶ ) copies/blood drop]. Receiver operator characteristic analysis demonstrated that capillary miR-122 sensitively and specifically reported DILI (area under the curve: 0.96, P = 0.0002).

CONCLUSION

This work supports the potential use of miR-122 as biomarker of human DILI when measured in a capillary blood drop. With development across DILI aetiologies, this could be used by novel point-of-care technologies to produce a minimally invasive, near-patient, diagnostic test.

Exosomes: A Rising Star in Falling Hearts

Although exosomes were previously recognized as a mechanism for discharging useless cellular components, growing evidence has elucidated their roles in conveying information between cells. They contribute to cell-cell communication by carrying nucleic acids, proteins and lipids that can, in turn, regulate behavior of the target cells. Recent research suggested that exosomes extensively participate in progression of diverse cardiovascular diseases (CVDs), such as myocardial infarction, cardiomyopathy, pulmonary arterial hypertension and others. Here, we summarize effects of exosome-derived molecules (mainly microRNAs and proteins) on cardiac function, to examine their potential applications as biomarkers or therapeutics in CVDs.

Interfacial Phenomena and Fluid Control in Micro/Nanofluidics

Fundamental aspects of rapidly advancing micro/nanofluidic devices are reviewed from the perspective of liquid interface chemistry and physics, including the influence of capillary pressure in microfluidic two-phase flows and phase transitions related to capillary condensation.

Vacuum-driven power-free microfluidics utilizing the gas solubility or permeability of polydimethylsiloxane (PDMS)

Suitable pumping methods for flow control remain a major technical hurdle in the path of biomedical microfluidic systems for point-of-care (POC) diagnostics. A vacuum-driven power-free micropumping method provides a promising solution to such a challenge. In this review, we focus on vacuum-driven power-free microfluidics based on the gas solubility or permeability of polydimethylsiloxane (PDMS); degassed PDMS can restore air inside itself due to its high gas solubility or gas permeable nature. PDMS allows the transfer of air into a vacuum through it due to its high gas permeability. Therefore, it is possible to store or transfer air into or through the gas soluble or permeable PDMS in order to withdraw liquids into the embedded dead-end microfluidic channels. This article provides a comprehensive look at the physics of the gas solubility and permeability of PDMS, a systematic review of different types of vacuum-driven power-free microfluidics, and guidelines for designing solubility-based or permeability-based PDMS devices, alongside existing applications. Advanced topics and the outlook in using micropumping that utilizes the gas solubility or permeability of PDMS will be also discussed. We strongly recommend that microfluidics and lab-on-chip (LOC) communities harness vacuum energy to develop smart vacuum-driven microfluidic systems.

Sensitive and multiplexed on-chip microRNA profiling in oil-isolated hydrogel chambers

Although microRNAs (miRNAs) have been shown to be excellent indicators of disease state, current profiling platforms are insufficient for clinical translation. Here, we demonstrate a versatile hydrogel-based microfluidic approach and novel amplification scheme for entirely on-chip, sensitive, and highly specific miRNA detection without the risk of sequence bias. A simulation-driven approach is used to engineer the hydrogel geometry and the gel-reaction environment is chemically optimized for robust detection performance. The assay provides 22.6 fM sensitivity over a three log range, demonstrates multiplexing across at least four targets, and requires just 10.3 ng of total RNA input in a 2 hour and 15 minutes assay.