Dialysis assisted ligand exchange on gold nanorods: Amplification of the performance of a lateral flow immunoassay for E. coli O157:H7

Abstract

Ligand exchange on the surface of gold nanorods (AuNRs) is widely used, but conventional methods usually require multiple centrifugation cycles to completely remove cetyltrimethylammonium bromide (CTAB). This can lead to undesired aggregation of AuNRs. A dialysis-assisted protocol is described here for ligand exchange on AuNRs. Dialysis driven by a concentration gradient is shown to be a powerful tool to separate CTAB from aqueous solutions. The concentration gradient of CTAB in a dialysis bag can avoid the possible aggregation of AuNRs that can be caused by drastic environmental changes. It also supports the rate of ligand exchange on the surfaces of the AuNRs. The modified AuNRs were employed in a lateral-flow test strip immunoassay (LFTS-IAs) for the food pathogen E. coli O157:H7 in order to study of efficiency of ligand exchange. Compared to AuNRs where ligand exchange was performed via multiple centrifugation cycles, the AuNRs prepared by dialysis-assisted ligand exchange show improved conjugation to antibody and enhanced visual signals in the test line of the LFTS-IAs. A portable strip reader (absorption wavelength = 525 nm) is used to records the testing results. The sensitivity of AuNRs modified by dialysis has been achieved even as low as 1 × 10 cfu·mL in a short time (within 15 min), and the working range is 1 × 10 to 1 × 10 cfu·mL, which is superior over the detection performance of conventional test strip using AuNRs modified by centrifugation. Graphical abstract Schematic presentation of the ligand exchange of AuNRs. The AuNRs were dialysed in water to decrease the CTAB concentration. Then, 11-mercaptoundecanoic acid (MUA) replaces the CTAB capped on the surface of AuNRs. The modified AuNRs were employed in a lateral flow immunoassay for E. coli O157:H7.

A review on advances in methods for modification of paper supports for use in point-of-care testing

“…A wax-based technology was applied to modify hydrophobic patterns and hydrophobic barriers on paper using a wax printer [27] and a pen-writing approach [28]. Different nanomaterials, such as quantum dots (QDs) [29][30][31][32][33], gold nanoparticles (AuNPs) [24,[34][35][36][37][38][39][40][41][42][43][44][45][46], AuNFs MBA @Ag [47] Cu-Pd/rGO nanoparticles [48], upconverting fluorescent nanocrystals [49], metal-organic framework [50], fluorescent nanoparticles [51], gold nanocage [52], gold nanorods [53], multi-walled carbon nanotubes and graphene oxide [54] and polymer nanoparticles [55], have also been used as reading signal in paper-based POCT devices. The functional papers prepared by these advanced modification approaches significantly extend the application potential of paper as the substrate of POCT devices.…”

Review of recent advances in improved lateral flow immunoassay for the detection of pathogenic Escherichia coli O157:H7 in foods

“…This treatment can lead to undesired aggregation of AuNRs. A dialysis‐assisted protocol was described by Tao et al (2018) for preparing ligand exchange on AuNRs. The modified AuNRs were employed in a LFIA (named LFTS‐IAs) strip for the foodborne E. coli O157:H7 detection.…”

“…The modified AuNRs were employed in a LFIA (named LFTS‐IAs) strip for the foodborne E. coli O157:H7 detection. Sensitivity of the dialysis AuNRs used in E. coli O157:H7 detection was as low as 1 × 10 2 cfu/ml in milk within 15 min reaction, this is superior over the detection performance of LFIA using the prepared AuNRs by centrifugation (Tao et al, 2018).…”

Enhancing the Sensitivity of Lateral Flow Immunoassay by Magnetic Enrichment Using Multifunctional Nanocomposite Probes

“…In addition, purification of the target analyte in the liquid sample by a separation technique is often required to improve the sensitivity and reliability. Among the various strategies proposed for analyte enrichment/purification to enhance the LFIA sensitivity, such as centrifugation-based methods, − magnetic separation, ,− and dialysis, magnetic separation is considered to be the most effective enrichment/purification method that is suitable for on-site analysis of an ultratrace amount of an analyte in a relatively large volume (>1 mL) of a mixed liquid sample, such as pathogens/hazardous chemicals in wastewater and cancer markers in urine.…”