Enhancing Point-of-Care Diagnosis of African Swine Fever Virus (ASFV) DNA with the CRISPR-Cas12a-Assisted Triplex Amplified Assay.

Accurate, ultrasensitive, and point-of-care (POC) diagnosis of the African swine fever virus (ASFV) remains imperative to prevent its spread and limit the losses incurred. Herein, we propose a CRISPR-Cas12a-assisted triplex amplified colorimetric assay for ASFV DNA detection with ultrahigh sensitivity and specificity. The specific recognition of recombinase aided amplification (RAA)-amplified ASFV DNA could activate the Cas12a/crRNA/ASFV DNA complex, leading to the digestion of the linker DNA (bio-L1) on magnetic beads (MBs), thereby preventing its binding of gold nanoparticles (AuNPs) network. After magnetic separation, the release of AuNPs network comprising a substantial quantity of AuNPs could lead to a discernible alteration in color and significantly amplify the plasmonic signal, which could be read by spectrophotometers or smartphones. By combining the RAA, CRISPR/Cas12a-assisted cleavage, and AuNPs network-mediated colorimetric amplification together, the assay could detect as low as 0.1 copies/µL ASFV DNA within 1 h. The assay showed an accuracy of 100% for the detection of ASFV DNA in 16 swine tissue fluid samples, demonstrating its potential for on-site diagnosis of ASFV.

Colorimetric Detection of Met Dimerization on Live Cells via Smartphone for High-Sensitivity Sensing of the HGF/Met Signaling Pathway.

Membrane protein dimerization regulates numerous cellular biological processes; therefore, highly sensitive and facile detection of membrane protein dimerization are very crucial for clinical diagnosis and biomedical research. Herein, a colorimetric detection of Met dimerization on live cells via smartphone for high-sensitivity sensing of the HGF/Met signaling pathway was developed for the first time. The Met monomers on live cells were recognized by specific ligands (aptamers) first, and the Met dimerizations triggered the proximity-ligation-assisted catalytic hairpin assembly (CHA) reaction to generate large amounts of G-quadruplex (G4) fragments which can further combine hemin to form G4/hemin DNAzymes possessing the horseradish-peroxidase-like catalytic activity for catalyzing the oxidation of ABTS by H2O2 and producing the colorimetric signal (i.e., color change). The colorimetric detection of Met on live cells was then achieved by image acquisition and processing via a smartphone. As a proof-of-principle, the HGF/Met signaling pathway based on Met-Met dimerization was facile monitored, and the human gastric cancer cells MKN-45 with natural Met-Met dimers were sensitively tested and a wide linear working range from 2 to 1000 cells with a low detection limit of 1 cell was obtained. The colorimetric assay possesses a good specificity and high recovery rate of MKN-45 cells spiked in peripheral blood, which indicates that the proposed colorimetric detection of Met dimerization can be used for convenient observation of the HGF/Met signaling pathway and has extensive application prospects in point-of-care testing (POCT) of Met-dimerization-related tumor cells.

Colorimetric Sensor for Online Accurate Detection of Breath Acetone.

Breath acetone (BrAce) is a validated biomarker of lipid oxidation and has been extensively studied for many applications, such as monitoring ketoacidosis in diabetes, guiding ketogenic diet, and measuring fat burning during exercise. Although many sensors have been reported for BrAce measurement, most of the contributions tested only synthetic or spiked breath samples, because of the complex components of human breath. Here, we show that online accurate detection of BrAce can be achieved using a colorimetric sensor. The high selectivity is enabled by the specific reaction between acetone and hydroxylamine sulfate, and the sensor has a high agreement with a reference instrument in ketosis monitoring. We anticipate that the colorimetric acetone sensor can be applied to various health-related applications.

A Paper Based Milli-Cantilever Sensor for Detecting Hydrocarbon Gases via Smartphone Camera.

Hydrocarbon gases, especially toxic ones like benzene and xylene, pose threats to human health and the environment. But existing detection techniques, like bulky GC-MS or portable PID, cannot fulfill people's requirement of affordable and reliable hydrocarbons monitoring for the purpose of personal exposure assessment. Here, a simple, low cost, and light hydrocarbon gases sensor using a smartphone camera as a readout was developed based on the paper based milli-cantilever bending induced by polymer swelling. Its sensing cantilever was composed of three layers: functional layer of polyethylene film, adhesive layer of double-side tape, and a substrate of weighing paper. And the dimensions of the milli-fabricated sensing cantilever are 8 mm long, 0.5 mm wide, and 50 µm thick. The sensor response was the displacement of milli-cantilever free end. As proof of concept, its performance to typical hydrocarbons of xylene, hexane, and BTEX was carefully examined. For all of them, the sensor showed good performance of linear response to hydrocarbon concentrations, wide detection range, low detection, and fast response. Taking xylene for example, the sensor showed wide detection range of 15-140 ppm, low detection limit of 15 ppm, and fast response of 30 s. The sensor cross-sensitivity to other hydrocarbons was consistent with polymer swelling theory that the more carbons the hydrocarbon has, the higher the sensor sensitivity. Taking advantage of the rough materials chosen and simple fabrication procedure, the developed sensors also had high stability with time, low cost, and good uniformity. The developed sensor is affordable both physically and financially, has good performance, could meet hydrocarbons monitoring requirements for occupational safety or air pollution in petroleum industry, and would benefit people's health.

Integrating Electrochemical and Colorimetric Sensors with a Webcam Readout for Multiple Gas Detection.

Multisensor detectors have merits of low cost, compact size, and capability of supplying accurate and reliable information otherwise hard to obtain by any single sensors. They are therefore highly desired in various applications. Despite the advantages and needs, they face great challenges in technique especially when integrating sensors with different sensing principles. To bridge the gap between the demand and technique, we here demonstrated an integration of electrochemical and colorimetric sensors with a webcam readout for multiple gas detection. Designed with two parallel gas channels but independent sensor cells, the dual-sensor detector could simultaneously detect each gas from their gas mixture by analysis of the group photo of the two sensors. Using Ag electro-dissolution as reporter, the bipolar electrochemical sensor achieved quantitative analysis for the first time thanks to application of pulse voltage. The sacrificed Ag layer used in the bipolar electrochemical (EC) sensor was recycled from CD, which further decreased the sensor cost and supplied a new way of CD recycling. The EC O2 sensor response, edge displacement of Ag layer due to electrochemical dissolution, has a linear relationship with O2 concentration ranging from 0 to 30% and has good selectivity to common oxidative gases. The colorimetric NO2 sensor linearly responded to NO2 concentrations ranging from 0 to 230 ppb with low detection limit of 10 ppb, good selectivity, and humidity tolerance. This integration method could be extended to integrating other gas sensors.

Light-Controlled Configurable Colorimetric Sensing Array.

Colorimetry is a popular gas-sensing platform, but it is typically limited to one-time use only. Here, we introduce a light-controlled configurable colorimetric sensing array to overcome this limitation. It features a photoactivated reaction between an analyte and a sensing material, such that sensing of an array element can be turned on and off with light. By sequential turning on of each array element, the sensor array can be used multiple times as determined by the number of array elements. This is analogous to a data storage device, which lasts until every storage element is used up. The total number of array elements and the area of each array element are configurable with light. With use of a smartphone screen as a programmable light source, we applied the sensing platform to the detection of oxygen gas and studied the relationship between sensitivity, noise, detection time, and array size. The relationship can be used to configure the array to meet the specifications of different applications.

Chemical Sensing in Real Time with Plants Using a Webcam.

It has been established that plants can smell and respond to chemicals in order to adapt to and survive in a changing chemical environment. Here we show that a plant responds to chemicals in air, and the response can be detected rapidly to allow tracking of air pollution in real time. We demonstrate this capability by detecting subtle color and shape changes in the leaves of mosses upon exposure to sulfur dioxide in air with a simple webcam and an imaging-processing algorithm. The leaves of mosses consist of a monolayer of cells, providing a large surface-to-volume ratio for highly sensitive chemical sensing. The plant sensor responds linearly to sulfur dioxide within a wide concentration range (0-180 ppm), and it can tolerate humidity variation (15-85% relative humidity) and chemical interference and regenerate itself. We envision that plants can help alert chemical exposure danger as a part of our living environment using low-cost CMOS imagers, and their chemical-sensing capabilities may be further improved with genetic engineering.

Gradient-Based Colorimetric Sensors for Continuous Gas Monitoring.

Colorimetry detects a color change resulted from a chemical reaction or molecular binding. Despite its widespread use in sensing, continuous monitoring of analytes with colorimetry is difficult, especially when the color-producing reaction or binding is irreversible. Here, we report on a gradient-based colorimetric sensor (GCS) to overcome this limitation. Lateral transport of analytes across a colorimetric sensor surface creates a color gradient that shifts along the transport direction over time, and GCS tracks the gradient shift and converts it into analyte concentration in real time. Using a low cost complementary metal-oxide semiconductor imager and imaging processing algorithm, we show submicrometer gradient shift tracking precision and continuous monitoring of ppb-level ozone.

High Performance Colorimetric Carbon Monoxide Sensor for Continuous Personal Exposure Monitoring.

Carbon monoxide (CO) is a highly poisonous gas, which can cause serious health risk. CO monitoring helps protect us from excessive exposure at home and in the workplace, and reduce occupation-related health risks for workers. Conventional electrochemical and metal oxide semiconductors (MOS) based CO sensors have been widely used, but the drawbacks such as poor selectivity and calibration burden also limit their applications, e.g., as wearable exposure monitors. Aiming at the reliable, miniaturized, and easy-to-use personal exposure device development, we report a colorimetric CO sensing platform, which achieves a detection limit of 1 ppm, dynamic range of 0-500 ppm, and high selectivity to CO over common interferents in air, such as CO2, NO2, SO2, and O3. This optical sensing platform can be expanded to other air pollutants by adding other chemical sensing probes. We believe the new sensing platform we introduced can provide a potential high performance sensing unit for wearable personal exposure assessment devices.

Oxygen Sensing Based on the Yellowing of Newspaper.

Newspaper is known to turn yellow over time. We show here that this yellowing process is sensitive to oxygen when exposed to UV light, leading to oxygen sensing. Oxygen sensing is critical to many applications, including industrial process control and breath analysis, but the existing oxygen sensors have limitations, especially for breath analysis that operates at 100% humidity. The UV irradiation also triggers fluorescence emission from newspaper, and the fluorescence intensity depends on oxygen concentration, providing an additional oxygen sensing method. Newspaper is stable in ambient air, and reactive to oxygen only with UV activation, which overcomes the instability issue of a typical colorimetric sensor in ambient air. The newspaper oxygen sensor works in 100% relative humidity air, containing various interferents. These unique properties of newspaper promise low cost and reliable oxygen sensing applications.

Measurement of the rate of water translocation through carbon nanotubes.

We present an approach for measuring the water flow rate through individual ultralong carbon nanotubes (CNTs) using field effect transistors array defined on individual tubes. Our work exhibits a rate enhancement of 882-51 and a slip length of 53-8 nm for CNTs with diameters of 0.81-1.59 nm. We also found that the enhancement factor does not increase monotonically with shrinking tube diameter and there exists a discontinuous region around 0.98-1.10 nm. We believe that these single-tube level results would help understand the intrinsic nanofluidics of water in CNTs.

Reflectance spectra of individual single-walled carbon nanotubes.

We report backscattering spectroscopic measurements on individual single-walled carbon nanotubes (SWNTs). The reflectance spectra show geometry-dependent resonant peaks corresponding to optical transitions between Van Hove singularities in the SWNTs' joint density of states. All nanotubes display certain colours as their reflectance spectra demonstrate strong energy dependence. This approach was proved to be an effective tool for probing the geometric structures and optical properties of individual SWNTs.