Mobile Phone Ratiometric Imaging Enables Highly Sensitive Fluorescence Lateral Flow Immunoassays without External Optical Filters

Abstract

Paper-based diagnostic tests based on the lateral flow immunoassay concept promise low-cost, point-of-care detection of infectious diseases, but such assays suffer from poor limits of detection. One factor that contributes to poor analytical performance is a reliance on low-contrast chromophoric optical labels such as gold nanoparticles. Previous attempts to improve the sensitivity of paper-based diagnostics include replacing chromophoric labels with enzymes, fluorophores, or phosphors at the expense of increased fluidic complexity or the need for device readers with costly optoelectronics. Several groups, including our own, have proposed mobile phones as suitable point-of-care readers due to their low cost, ease of use, and ubiquity. However, extant mobile phone fluorescence readers require costly optical filters and were typically validated with only one camera sensor module, which is inappropriate for potential point-of-care use. In response, we propose to couple low-cost ultraviolet light-emitting diodes with long Stokes-shift quantum dots to enable ratiometric mobile phone fluorescence measurements without optical filters. Ratiometric imaging with unmodified smartphone cameras improves the contrast and attenuates the impact of excitation intensity variability by 15×. Practical application was shown with a lateral flow immunoassay for influenza A with nucleoproteins spiked into simulated nasal matrix. Limits of detection of 1.5 and 2.6 fmol were attained on two mobile phones, which are comparable to a gel imager (1.9 fmol), 10× better than imaging gold nanoparticles on a scanner (18 fmol), and >2 orders of magnitude better than gold nanoparticle-labeled assays imaged with mobile phones. Use of the proposed filter-free mobile phone imaging scheme is a first step toward enabling a new generation of highly sensitive, point-of-care fluorescence assays.

An amphiphilic-ligand-modified gold nanoflower probe for enhancing the stability of lateral flow immunoassays in dried distillers grains

“…As demonstrated in Fig. 2A and B, both N-AuNF-Abs and Tr-AuNF-Abs showed high colloidal stability in the presence of a wide range pH values (4)(5)(6)(7)(8)(9)(10)(11). The results in Fig.…”

“…The results in Fig. S9A and B † demonstrate that the two ZEN-LFA strips showed similar changes in their OD T and OD C responses with changing pH values (4)(5)(6)(7)(8)(9)(10)(11), which may account for the inuence of the pH value on the antigen-antibody interaction on the T line and C line. As shown in Fig.…”

“…Lateral ow immunoassays (LFAs) are powerful tools for on-site screening detection in clinical diagnosis, environmental analysis, and food safety monitoring because of their simplicity, rapid results, cost-effectiveness, and user-friendliness. [1][2][3][4][5] Currently, various nanomaterials, including light absorbing nanoparticles [6][7][8] (e.g., gold nanoparticles (AuNPs), carbon nanoparticles, and colloidal selenium), light emitting nanoparticles [9][10][11][12][13] (e.g., dye-doped uorescent beads, time-resolved uorescent beads, quantum dot beads, and up-converting phosphor nanoparticles), and magnetic nanoparticles, 14 have been widely used as labels in LFAs. Among them, AuNPs are the most popular signal reporter in commercial LFAs because of their facile synthesis and modication, biocompatibility and low toxicity, low cost, and naked eye detectable results.…”

An RGB-emitting molecular cocktail for the detection of bacterial fingerprints

“…We further developed a logistic regression model that connected RGB values to the different types of cases. 42 A regression equation for use with the Microcolor system that would optimally predict the risk of developing OSCC is listed in Fig. 5D.…”

Development of a smartphone-based rapid dual fluorescent diagnostic system for the simultaneous detection of influenza A and H5 subtype in avian influenza A-infected patients

“…Various fluorescent materials have been applied for lateral flow assays as alternative to conventional gold nanoparticles to detect influenza A as POCT [11][12][13][14][15][16]. Also, self-contained and disposable diagnostic devices have been developed [15,[17][18][19].…”