Magnetic-optical nanohybrids for targeted detection, separation, and photothermal ablation of drug-resistant pathogens

Abstract

A rapid, sensitive and quantitative immunoassay for the targeted detection and decontamination of E. coli based on Fe3O4 magnetic nanoparticles (MNPs) and plasmonic popcorn-shaped gold nanostructure attached single-walled carbon nanotubes (AuNP@SWCNT) is presented. The MNPs were synthesized as the support for a monoclonal antibody (mAb@MNP). E. coli (49979) was captured and rapidly preconcentrated from the sample with the mAb@MNP, followed by binding with Raman-tagged concanavalin A-AuNP@SWCNTs (Con A-AuNP@SWCNTs) as detector nanoprobes. A Raman tag 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) generated a Raman signal upon 670 nm laser excitation enabling the detection and quantification of E. coli concentration with a limit of detection of 10(2) CFU mL(-1) and a linear logarithmic response range of 1.0 × 10(2) to 1.0 × 10(7) CFU mL(-1). The mAb@MNP could remove more than 98% of E. coli (initial concentration of 1.3 × 10(4) CFU mL(-1)) from water. The potential of the immunoassay to detect E. coli bacteria in real water samples was investigated and the results were compared with the experimental results from the classical count method. There was no statistically significant difference between the two methods (p > 0.05). Furthermore, the MNP/AuNP@SWCNT hybrid system exhibits an enhanced photothermal killing effect. The sandwich-like immunoassay possesses potential for rapid bioanalysis and the simultaneous biosensing of multiple pathogenic agents.

Figure 1

TEM images of (A) MNP, (B) APTES@MNP core−shell structures. (C) Histogram of hydrodynamic diameter of MNP (D) FTIR spectra of MNPs before (black) and after (red) APTES modification

Figure 2

(A) Surface charge characteristics of additional layer components on the MNP (B) Effect of number of washing cycles on binding efficiency. (Error bars indicate the standard deviation obtained from three measurements).

Figure 3

TEM images of (A) AuNPs, (B) f-SWCNTs, (C) mannose-AuNP@SWCNTs

Figure 4

Absorption spectra of (A) f-SWCNT (black), mannose-AuNP@SWCNTs (blue), Nanoprobes (red), and (B) Nanoprobes (red), Nanoprobes in the presence of E. coli (black).

Figure 5

TEM image of (a) E. coli captured by mAb-MNPs (b) E. coli captured by nanoprobes (c) immunocomplex (d) Digital photograph showing magnetic separation of E.coli bound MNP/Nanoprobe immunocomplex.

Figure 6

SERS spectra of different concentrations of E. coli in (A) DTNB-tagged con A-AuNP@SWCNT (B) the sandwich immunoassay (20 mW excitation power, 30 s acquisition time), (C) Linear fitting of the peak intensities at 1348 cm⁻¹ as a function of the logarithm of E. coli concentration (High resolution SERS spectral region between 1300–1420 cm⁻¹). Error bars indicate the standard deviation obtained from three measurements.

Figure 7

(A) Digital photographs of colonies of sandwiched E. coli when exposed to NIR light for varied length of times (B) Scatter plots showing viability (%) of untreated and differently treated E. coli when exposed to NIR. (Error bars indicate the standard deviation obtained from three measurements).