Fig. 5: Bioengineering next-generation lateral flow tests.

a, Cas-based reactions can be combined with a nanozyme-amplified lateral flow test (LFT). Target RNA is mixed with the guiding RNA (gRNA)–Cas13 complex and reporter RNA to trigger the clustered regularly interspaced short palindromic repeats (CRISPR) reaction. Subsequently, streptavidin-functionalized nanozymes are mixed with the CRISPR reaction product that contains the biotinylated reporter RNA to form a complex. The test strip is preprinted with anti-fluorescein amidite to draw up the mixture. The uncleaved reporter RNA–nanozyme complexes are captured at the test line. Finally, the substrate is added for colour development. b, Spin-enhanced quantum nanodiamond sensing and background subtraction can be implemented in LFTs to enable ultra-sensitive virus detection. The scanning electron micrographs show nanodiamonds. Pixel intensity variation is shown at the test line on an LFT strip with immobilized nanodiamonds under an amplitude-modulated microwave field. Background subtraction allows ultra-sensitive virus detection. In the amplitude-modulated field, mean fluorescence intensity varies over time. A lock-in algorithm quantifying modulation amplitude over a range of frequencies, gives a sinc function with a peak at the modulation frequency. Nanodiamonds are immobilized at the test line in a sandwich structure in the presence of double-stranded DNA (dsDNA) amplicons. AU, arbitrary units. c, Healthcare workers collect images of human immunodeficiency virus (HIV) LFTs in the field, and machine learning allows automatic classification of LFT results. d, Deep-learning-enabled point-of-care sensing using multiplex paper-based sensors and a mobile-phone reader with an inserted vertical flow assay cassette. The algorithmically determined immunoreaction spot layout of the multiplexed vertical flow assay membrane contains several distinct spotting conditions, each of which uniquely reacts with the sensed analyte and the signal-forming gold nanoparticles. CN/DAB; 4-chloro-1-naphthol/3,3′-diaminobenzidine, tetrahydrochloride. Part a adapted from ref. 131, Springer Nature Limited. Part b adapted with permission from ref. 138, Elsevier, adapted from ref. 13, Springer Nature Limited, and reprinted from ref. 13, Springer Nature Limited. Part c image courtesy of African Health Research Institute. Part d adapted from ref. 165, Springer Nature Limited.