Highly sensitive β-galactosidase detection using streptavidin-display E. coli and lateral flow immunoassay

Lateral flow immunoassay (LFIA) is a detection method widely used in biomedicine, agriculture, food, and environmental sciences and has the advantages of speed, simplicity, and low cost. However, the poor detection limit of LFIA hinders its application. In this study, we constructed a streptavidin-display E. coli strain to improve the sensitivity of LFIA. Gold nanoparticles (AuNPs) were used as the detected labels and recombinant E. coli binding biotinylated anti-target antibodies served as a signal amplifier. For detection of β-galactosidase, the model protein used in this study, the detection limit was about 5 * 10−15 mol (5 *10−11 M), while that of the conventional LFIA is about 10−12 mol (10−8 M). Having AuNP as the detected label improved LFIA sensitivity 200-fold without sacrificing its advantages and the data interpretation was the same as the traditional LFIA. We further expressed enhanced green fluorescent protein (eGFP) inside the streptavidin-displayed E. coli. Without AuNPs, the fluorescent E. coli acted as a very strong signal, which could be detected by a fluorescence detector, such as a fluorescence microscope. Using the eGFP E. coli as the signal, the detection limit was about 5 * 10−18 mol (5 *10−14 M). This is 2 * 105-fold and 1000-fold better than the AuNP results for the conventional, and proposed method, respectively. However, the method using eGFP is a better fit for lab-use than for point-of-care because of the need for a fluorescence detector and different data interpretation compared with the traditional LFIA. These assays are very promising, especially for rapid screening of proteins as biomarkers. [Display omitted] •A new test kit that combines streptavidin-display E. coli system with LFIA assay for rapid protein detection was developed.•Compared with traditional LFIA, the LOD of the proposed method using AuNPs and eGFP is 200 and 200,000 times better.•The results could be observed directly by naked eye and fluorescence detector.•The proposed method using AuNP and E. coli in this study improves LFIA sensitivity without sacrificing its advantages.