Detection of E. coli labeled with metal-conjugated antibodies using lateral-flow assay and laser-induced breakdown spectroscopy

Authors: GONDHALEKAR, C - Purdue University; BIELA, E - Purdue University; RAJWA, B - Purdue University; PATSEKIN, V - Purdue University; STURGIS, J - Purdue University; REYNOLDS, C - Purdue University; DOH, I - Purdue University; DIWAKAR, P - Purdue University; STANKER, L - Purdue University; ZORBA, V - Purdue University; MAO, X - Purdue University; RUSSO, R - Purdue University; ROBINSON, J - Purdue University

Submitted to: Analytical and Bioanalytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2019
Publication Date: 1/27/2020
Citation: Gondhalekar, C., Biela, E., Rajwa, B.B., Patsekin, V., Sturgis, J., Reynolds, C., Doh, I.J., Diwakar, P., Stanker, L., Zorba, V., Mao, X., Russo, R., Robinson, J.P. 2020. Detection of E. coli labeled with metal-conjugated antibodies using lateral-flow assay and laser-induced breakdown spectroscopy. Analytical and Bioanalytical Chemistry. 412:1291-1301. https://doi.org/10.1007/s00216-019-02347-3.
DOI: https://doi.org/10.1007/s00216-019-02347-3

Interpretive Summary: Sensitive and specific detection of human pathogens using rapid assays remains a major goal of food safety research. Traditionally, these procedures utilize a colorimetric readout in a lateral flow assay (LFA) that uses a capillary wicking action to move reagents passively through a test strip. LFA assays are limited in multiplexing (ability to detect more than one reagent) and sensitivity (as they rely on the appearance of contrasting color lines). This report describes a new method for labeling reagents with rare-earth metals and detecting them with laser-induced breakdown spectroscopy (LIBS). Replacing simple colorimetric intensity readout with a spectroscopic device provides multiple opportunities to make the LFA assays more sophisticated and capable of simultaneously reporting numerous targets. This system allows the creation of more sensitive and flexible assays that would be useful to the food industry or food regulatory agencies.

Technical Abstract: This study explores the adoption of laser-induced breakdown spectroscopy (LIBS) for the analysis of lateral-flow immunoassays (LFIAs). Gold (Au) nanoparticles are standard biomolecular labels among LFIAs, typically detected via colorimetric means. A wide diversity of lanthanide-complexed polymers (LCPs) are also used as immunoassay labels but are inapt for LFIAs due to lab bound detection instrumentation. This is the first study to show the capability of LIBS to transition LCPs into the realm of LFIAs, and one of the few to apply LIBS to biomolecular label detection in complete immunoassays. Initially, an in-house LIBS system was optimized to detect an Au standard through a process of line selection across acquisition delay times, followed by determining limit of detection (LOD). The optimized LIBS system was applied to Au-labeled Escherichia coli detection on a commercial LFIA; comparison with colorimetric detection yielded similar LODs (1.03E4 and 8.890E3 CFU/mL respectively). Optimization was repeated with lanthanide standards to determine if they were viable alternatives to Au labels. It was found that europium (Eu) and ytterbium (Yb) may be more favorable biomolecular labels than Au. To test whether Eu-complexed polymers conjugated to antibodies could be used as labels in LFIAs, the conjugates were successfully applied to E. coli detection in a modified commercial LFIA. The results suggest interesting opportunities for creating highly multiplexed LFIAs. Multiplexed, sensitive, portable, and rapid LIBS detection of biomolecules concentrated and labeled on LFIAs is highly relevant for applications like food safety, where in-field food contaminant detection is critical