Using Bioconjugated Nanoparticles To Monitor E. coli in a Flow Channel

Abstract

A simple and portable flow channel optical detection system combined with bioconjugated luminescent nanoparticles allows the rapid detection of single bacterial cells without sample enrichment. The optical system is designed to have single-molecule-detection capability in a microcapillary flow channel by decreasing the laser excitation probe volume to a few picoliters, which consequently results in a low background. Specific monoclonal antibodies were immobilized on nanoparticles to form nanoparticle-antibody conjugates. The bioconjugated nanoparticles bind to the target bacteria when they recognize the antigen on the bacterium surface, thus providing a bright luminescent signal for the detection of individual bacteria cells. The high sensitivity provided by the luminescent and photostable silica nanoparticles eliminates the need for further enrichment of bacteria samples and signal amplification. This flow channel detection system is convenient and allows the detection of single bacterial cells within a few minutes.

Nanomaterials in fluorescence-based biosensing

“…Another type of fluorescent nanomaterial which has been extensively tested as a labeling reagent in the detection of pathogens, nucleic acids, and proteins is silica nanoparticles doped with organic dyes [20][21][22][23][24][25]. This type of nanomaterial has the following advantages in biosensing: (1) silicon is abundant and nontoxic; (2) the high surface-to-volume ratio of the nanoparticles facilitates their binding to biomolecules; (3) the inclusion of a large number of fluorescent dye molecules inside each nanoparticle results in excellent photostability due to the ability of the silica matrix to shield from molecular oxygen, and the inclusion also dramatically increases the dye-to-biomolecule labeling ratio, leading to high signal amplification factors during detection; and (4) silica is relatively inert in chemical reactions, but still allows surface modification with wellestablished chemistries [20,21].…”

Bioconjugated silica nanoparticles: Development and applications

“…This method is capable of determining the existence of a single bacterium with 99.99% accuracy when compared to the widely used colony forming units/mL count (CFU) on agar plates. The results were further confirmed using a laboratorymade fl ow cytometer which precisely detected single bacterial cells with antibody-conjugated NPs bound to them and recoded the fluorescence spike when the cells flowed through the detection channel [63]. The total time for the sample detection and analysis with this fl ow system was only a few minutes, which minimized the duration of the bacteria assay even further.…”

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

“…Silica NPs are one of the fluorescent alternatives to QDs and this is primarily due to their ability to be doped with large quantities of fluorescent dyes. They have seen a variety of applications within direct bacteriological detection, including E. coli , Salmonella , DPA detection, LFAs, and FC. ,, Other NP materials utilized in biothreat agent detection include polystyrene, fluorescent AuNPs, upconverting rare earth metal NPs, and micelles . As mentioned, MNPs are often used in the detection of bioagents, in conjugation with optical probes such as TiO 2 for the detection of Salmonella or fluorescently labeled antibodies for E. coli O157 …”