COVID-19 necessitates the development of reliable and convenient diagnostic tools. In this work, a facile 3D-printed smartphone platform was constructed that achieved reliable visual detection of SARS-CoV-2 by eliminating the effect of ambient light and fixing the camera position relative to the sample. The oligonucleotide probe is modified with orange-red-emitting TAMRA working as an internal standard and green-emitting FAM serving as a sensitive sensing agent. Under 365-nm UV excitation, the emission wavelengths of TAMRA and FAM are 580 nm and 518 nm, respectively. When the probes interact with the targets, the green fluorescence gradually restores while the orange-red fluorescence remains stable. Thus, a striking color transition from orange-red to green could be observed by the naked eye. The detection limit of SARS-CoV-2 nucleic acid is 0.23 nM, and the entire process of color change could be completed in 25 min. Furthermore, the RGB value analysis of the sample solution was conducted using a smartphone for reliable and reproducible discrimination of SARS-CoV-2. The proposed smartphone platform might establish a general method for visual detection of SARS-CoV-2 nucleic acid as well as other virus-related diseases. Graphical abstract
An europium functionalized ZnO quantum dots (QDs) ratiometric fluorescent nanoprobe is designed to establish a real time, on-site visual, and highly sensitive probe method for tetracycline (TC). The yellow-emitting ZnO QDs serves as the internal reference, while the Eu 3+ chelated on the surface of ZnO QDs is used as the signal reporting unit. This nanoprobe exhibits rapid response, excellent selectivity, and high sensitivity with a detection limit of 4 nM in detecting the levels of TC. In addition, fluorescence of the nanoprobe can change from yellow to red as the concentration of TC increases. Thus, naked eye detection of TC was realized using the test paper processed by nanoprobe, followed by RGB value analysis function on the mobile phone APP.
Qian Zhao,Xinhui Xie,Liye Chen,Jiahao Wu,Ziping Jiang,Xingbo Shi
Aflatoxin B1 (AFB1), one of the most toxic mycotoxins, is commonly found in various food. This study develops a dual-mode biosensor integrating smartphone analysis and dark-field microscopy (DFM) observation for AFB1 detection based on the disintegration of core-shell Ag@Au nanoparticles (Ag@Au NPs). Employing a sandwich assay format, AFB1 aptamer assembled Ag@Au NPs are anchored on 96-well plate and disintegrated by nitric acid. Thereafter, the Ag core is etched, releasing Ag + that serve as colorimetric signal regulators upon the introduction of the glutathione-manganese dioxide nanosheets-3,3′,5,5′-tetramethylbenzidine substrate. The color signal is analyzed using a smartphone based on red-green-blue value analysis. Furthermore, the collapsed Au shell releases individual Au NPs that serve as dark-field scattering nanoprobes, producing a high-intensity green dark-field scattering signal under DFM observation. The detection limit (3.67 fg/mL) is 199/8174/2180-fold lower than those of colorimetric signal, commercial enzyme-linked immunosorbent assay kit, and high-performance liquid chromatography, respectively. Overall, smartphone analysis enables on-site preliminary screening without sophisticated instrumentation. DFM observation allows the ultra-sensitive quantitative detection in a laboratory. The proposed dual-mode biosensor will not only reduce false-positive/negative rate through the bidirectional signal readout, but also offer a practical, stable, and ultrasensitive strategy for AFB1 detection in food.
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