Point-of-care COVID-19 assays that are more sensitive than the current RT-PCR (reverse transcription polymerase chain reaction) gold standard assay are needed to improve disease control efforts. We describe the development of a portable, ultrasensitive saliva-based COVID-19 assay with a 15-min sample-to-answer time that does not require RNA isolation or laboratory equipment. This assay uses CRISPR-Cas12a activity to enhance viral amplicon signal, which is stimulated by the laser diode of a smartphone-based fluorescence microscope device. This device robustly quantified viral load over a broad linear range (1 to 105 copies/μl) and exhibited a limit of detection (0.38 copies/μl) below that of the RT-PCR reference assay. CRISPR-read SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) RNA levels were similar in patient saliva and nasal swabs, and viral loads measured by RT-PCR and the smartphone-read CRISPR assay demonstrated good correlation, supporting the potential use of this portable assay for saliva-based point-of-care COVID-19 diagnosis.

Developing easy-to-use and miniaturized detectors is essential for in-field monitoring of environmentally hazardous substances, such as the cyanotoxins. We demonstrated a differential fluorescent sensor array made of aptamers and single-stranded DNA (ssDNA) dyes for multiplexed detection and discrimination of four common cyanotoxins with an ordinary smartphone within 5 min of reaction. The assay reagents were preloaded and dried in a microfluidic chip with a long shelf life over 60 days. Upon the addition of analyte solutions, competitive binding of cyanotoxin to the specific aptamer-dye conjugate occurred. A zone-specific and concentration-dependent reduction in the green fluorescence was observed as a result of the aptamer conformation change. The aptasensors are fully optimized by quantification of their dissociation constants, tuning the stoichiometric ratios of reaction mixtures, and implementation of an internal intensity correction step. The fluorescent sensor array allowed for accurate identification and measurement of four important cyanotoxins, including anatoxin-a (ATX), cylindrospermopsin (CYN), nodularin (NOD), and microcystin-LR (MC-LR), in parallel, with the limit of detection (LOD) down to a few nanomolar (<3 nM), which is close to the World Health Organization's guideline for the maximum concentration allowed in drinking water. The smartphone-based sensor platform also showed remarkable chemical specificity against potential interfering agents in water. The performance of the system was tested and validated with real lake water samples that were contaminated with trace levels of individual cyanotoxins as well as binary, ternary, and quaternary mixtures. Finally, a smartphone app interface has been developed for rapid on-site data processing and result display.

In this work, we study the mechanical properties of sodium dodecylsulfate (SDS) and dodecylamine hydrochloride (DAH) micellar films at a graphite surface via atomic force microscopy (AFM). Breakthrough forces for these films were measured using silicon nitride cantilevers, and found to be 1.1 ±0.1 nN for a 10 mM DAH film and 3.0 ±0.3 nN for a 10 mM SDS film. For 10 mM SDS films, it was found that the addition of 1.5 mM of NaCl, Na 2 SO 4 , or MgCl 2 produced a 50-70% increase in measured breakthrough force. Similar results were found for 10 mM DAH films when NaCl and MgCl 2 were added. A model was developed, based upon previous work on lipid films and CMC data gathered via spectrofluorometry measurements, to produced the observed differences. The pH of the bulk solution was varied for both 10 mM SDS and DAH films, and was found to have little effect on breakthrough force.

Analysis on a single-cell basis is both fundamental and meaningful in biomedical research and clinical practice. Flow cytometry is one of the most popular approaches in this field with broad applications in cell sorting, counting, and identification of rare cells. However, the complicated design and bulky size of conventional flow cytometry have restricted their applications mainly in centralized laboratories. With the recent development of smartphone devices, smartphone-based cytometry has been explored and tested for single-cell analysis. Compared with traditional cytometers, smartphone-based cytometric biosensors are more suitable for point-of-care (POC) uses, such as on-site disease diagnosis and personal health monitoring. In this review article, the history of traditional flow cytometry is introduced, and advances of smartphone-enabled cytometry are summarized in detail based on different working principles. Representative POC applications of smartphone cytometers are also discussed. The achievements demonstrated so far illustrate the potential of smartphone-based cytometric devices to transform single-cell measurement in general, with a significant impact in POC diagnostics, preventive medicine, and cell biology.