Agarose-Droplet-Based Digital LAMP Assay for Counting Virus DNA in Single-Particle ICP-MS

Ultrasensitive and Wash-Free Detection of Tumor Extracellular Vesicles by Aptamer-Proximity-Ligation-Activated Rolling Circle Amplification Coupled to Single Particle ICP-MS

Tumor-derived extracellular vesicles (TEVs) are rich in cellular information and hold great promise as a biomarker for noninvasive cancer diagnosis. However, accurate measurement of TEVs presents challenges due to their low abundance and potential interference from a high number of EVs derived from normal cells. Herein, an aptamer-proximity-ligation-activated rolling circle amplification (RCA) method for EV membrane recognition, coupled with single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) for the quantification of TEVs, is developed. When DNA-labeled ultrasmall gold nanoparticle (AuNP) probes bind to the long chains formed by RCA, they aggregate to form large particles. Notably, small AuNPs scarcely produce pulse signals in sp-ICP-MS, thereby detecting TEVs in a wash-free manner. By leveraging the strong binding affinity of aptamers, dual aptamers for EpCAM and PD-L1 recognition, and the sp-ICP-MS technique, this method offers remarkable sensitivity and selectivity in tracing TEVs. Under optimized conditions, the present method shows a favorable linear relationship between the pulse signal frequency of sp-ICP-MS and TEV concentration within the range of 105-107 particles/mL, along with a detection limit of 1.1 × 104 particles/mL. The pulse signals from sp-ICP-MS combined with machine learning algorithms are used to discriminate cancer patients from healthy donors with 100% accuracy. Due to its simple and fast operation and excellent sensitivity and accuracy, this approach holds significant potential for diverse applications in life sciences and personalized medicine.

Single Particle Analysis-Enhanced DNA Walking Machine for Sensitive miRNA Detection

DNA walking machines have achieved significant breakthroughs in areas such as biosensing, bioimaging, and early cancer diagnosis, facilitated by the self-assembly of DNA or its combination with other materials, such as magnetic beads and metal nanoparticles. However, current DNA walking machine strategies are constantly challenged by inadequate analytical sensitivity, while sophisticated signal amplification procedures are often indispensable. Single-particle inductively coupled plasma mass spectrometry (SP-ICPMS) provides superior sensitivity and can effectively discriminate between background noise and detected signals due to the large number of metal atoms in a nanoparticle and the concentrating effect of single nanoparticle detection. In this study, we present a novel approach utilizing single nanoparticle counting and duplex-specific nuclease (DSN)-assisted signal amplification to construct a 3D DNA walking machine for detecting the aggressive prostate cancer (PCa) biomarker miRNA-200c. The proposed strategy showed an improvement in sensitivity with a detection limit (LOD) of 0.93 pM (28 amol) and was successfully applied in human serum samples. To the best of our knowledge, this is the first report of the DNA walking machine with single nanoparticle counting study.

Label-free detection of biomolecules using inductively coupled plasma mass spectrometry (ICP-MS)

Bioassays using inductively coupled plasma mass spectrometry (ICP-MS) have gained increasing attention because of the high sensitivity of ICP-MS and the various strategies of labeling biomolecules with detectable metal tags. The classic strategy to tag the target biomolecules is through direct antibody-antigen interaction and DNA hybridization, and requires the separation of the bound from the unbound tags. Label-free ICP-MS techniques for biomolecular assays do not require direct labeling: they generate detectable metal ions indirectly from specific biomolecular reactions, such as enzymatic cleavage. Here, we highlight the development of three main strategies of label-free ICP-MS assays for biomolecules: (1) enzymatic cleavage of metal-labeled substrates, (2) release of immobilized metal ions from the DNA backbone, and (3) nucleic acid amplification-assisted aggregation and release of metal tags to achieve amplified detection. We briefly describe the fundamental basis of these label-free ICP-MS assays and discuss the benefits and drawbacks of various designs. Future research is needed to reduce non-specific adsorption and minimize background and interference. Analytical innovations are also required to confront challenges faced by in vivo applications.

Simultaneous detection of dual microRNAs related to EV71 using ICP-MS based on metal nanoparticle labeling with hybridization chain reaction

BACKGROUND

Hand, foot, and mouth (HMFD) disease caused by enterovirus 71 (EV 71), is closely associated with severe clinical manifestations and can be deadly. Early detection of EV 71 can be achieved by detecting the increment in miR296 and miR16 in the serum. Using HCR to amplify signals and convert biological signals into metal nanoparticle signals detectable by ICP-MS is a detection method that can collect more accurate and reliable information, compared with traditional methods, in the detection of biological samples.

RESULTS

We described a strategy for the simultaneous detection of miR296 and miR16 by ICP-MS based on metal nanoparticles (NPs) labeling with HCR. Briefly, single-stranded DNA (ssDNA) and magnetic beads (MBs), as well as NPs and signal probes for miRNA (Sp-miR) were firstly conjugated via the streptavidin-biotin recognition system, constituting ssDNA-MBs and NPs-Sp-miR complex, respectively. The latter complex then hybridized with the former through HCR, generating the nanosensors for targets. Then, the targets were added and hybridized with ssDNA, and the HCR complex with NPs was released into the solution. Finally, the corresponding signals of the NPs were measured by ICP-MS. Results demonstrated that the developed method had good sensitivity and satisfactory selectivity and precision. Furthermore, when applied to biological samples with a complex matrix, the developed method also showed good recovery (88 % - 92 %) and reproducibility (RSD<10 %).

SIGNIFICANCE

This method contributes to the early diagnosis of HFMD and opens up ideas for the further development of high-throughput biomarker detection. The strategy has practical potential for miR296 and miR16 detection in biological samples and provides a promising tool for multiple miRNA detection.

Development and future of droplet microfluidics

Over the past two decades, advances in droplet-based microfluidics have facilitated new approaches to process and analyze samples with unprecedented levels of precision and throughput. A wide variety of applications has been inspired across multiple disciplines ranging from materials science to biology. Understanding the dynamics of droplets enables optimization of microfluidic operations and design of new techniques tailored to emerging demands. In this review, we discuss the underlying physics behind high-throughput generation and manipulation of droplets. We also summarize the applications in droplet-derived materials and droplet-based lab-on-a-chip biotechnology. In addition, we offer perspectives on future directions to realize wider use of droplet microfluidics in industrial production and biomedical analyses.

Design of a Digital LAMP Detection Platform Based on Droplet Microfluidic Technology

Loop-mediated isothermal amplification (LAMP) is a rapid and high-yield amplification technology for specific DNA or RNA molecules. In this study, we designed a digital loop-mediated isothermal amplification (digital-LAMP)-functioning microfluidic chip to achieve higher sensitivity for detection of nucleic acids. The chip could generate droplets and collect them, based on which we could perform Digital-LAMP. The reaction only took 40 min at a constant temperature of 63 °C. The chip enabled highly accurate quantitative detection, with the limit of detection (LOD) down to 10² copies μL^-1. For better performance while reducing the investment of money and time in chip structure iterations, we used COMSOL Multiphysics to simulate different droplet generation ways by including flow-focusing structure and T-junction structure. Moreover, the linear structure, serpentine structure, and spiral structure in the microfluidic chip were compared to study the fluid velocity and pressure distribution. The simulations provided a basis for chip structure design while facilitating chip structure optimization. The digital-LAMP-functioning chip proposed in the work provides a universal platform for analysis of viruses.

Bent-Capillary-Centrifugal-Driven Monodisperse Droplet Generator with Its Application for Digital LAMP Assay

We developed a bent-capillary-centrifugal-driven (BCCD) monodisperse droplet generator, which could achieve a perfect combination of driving and segmentation for the dispersed phase only using a rotating bent capillary immersed in the continuous phase (mineral oil). The sample could flow continuously to the bent-capillary outlet to form the droplet precursors, which were segmented into homogeneous droplets in the continuous phase. Through the investigation of influence factors on droplet size and stability, we found that the droplet size could be conveniently controlled by the rotational speed of the bent capillary. The droplet volumes could be adjusted with the range from 34 pL to 1 μL, and the coefficient variations (CVs) were less than 3%. Meanwhile, the BCCD droplet generator could realize the controllable droplet output with a high-efficiency sample utilization of 99.75 ± 1.15%, which offered a significant advantage in reducing the waste of precious samples in the droplet generation process. We validated this system with a digital loop-mediated isothermal amplification (dLAMP) assay for the absolute quantification of Mycobacterium tuberculosis complex nucleic acids. The results demonstrated that the BCCD droplet generator was easy to build, was of low cost, and was convenient to operate, as well as avoided sample loss and cross-contamination by coupling with a 96-well plate. Overall, the present platform, as a simple chip-free droplet generator, will provide an especially valuable droplet generation solution for biochemical applications based on droplets.

Gold Nanourchins Improve Virus Targeting and Plasmonic Coupling for Virus Diagnosis on a Smartphone Platform

Point-of-care detection of pathogens is critical to monitor and combat viral infections. The plasmonic coupling assay (PCA) is a homogeneous assay and allows rapid, one-step, and colorimetric detection of intact viruses. However, PCA lacks sufficient sensitivity, necessitating further mechanistic studies to improve the detection performance of PCA. Here, we demonstrate that gold nanourchins (AuNUs) provide significantly improved colorimetric detection of viruses in PCA. Using respiratory syncytial virus (RSV) as a target, we demonstrate that the AuNU-based PCA achieves a detection limit of 1400 PFU/mL, or 17 genome equivalent copies/μL. Mechanistic studies suggest that the improved detection sensitivity arises from the higher virus-binding capability and stronger plasmonic coupling at long distances (∼10 nm) by AuNU probes. Furthermore, we demonstrate the virus detection with a portable smartphone-based spectrometer using RSV-spiked nasal swab clinical samples. Our study uncovers important mechanisms for the sensitive detection of intact viruses in PCA and provides a potential toolkit at the point of care.

Standard-free single magnetic bead evaluation: a stable nanoplatform for prostate disease differentiation

Explicit interpretation of heterogeneity between prostate-specific antigen (PSA) subtypes is essential for prostate cancer differentiation during different disease courses, whereas a universal protocol with uniform criteria is still lacking across the globe. In this work, a standard-free single magnetic bead (SMB) nanoplatform utilizing metal nanoparticles with optimal diameters was proposed for prostate disease differentiation in a 134-donor model. The inaccuracy of detection in absolute quantification was diminished via evaluations of metal intensities on the single magnetic bead. The intrinsic proportion of fPSA in tPSA was successfully evaluated by direct use of the Pt to Au intensity ratio (Pt/Au ratio), exhibiting better differentiation between healthy and unhealthy, benign prostatic hyperplasia (BPH) and cancer individuals compared with solo fPSA or tPSA. We generated thresholds respectively for prostate disease differentiation, envisioning that this standard-free SMB nanoplatform would establish a standardized methodology with uniform criteria worldwide in cancer diagnosis, staging, and postoperative assessments.