Better biosensor

Many biosensor technologies rely on a correlation between analyte binding and luminescence fluctuations

Randall C Willis
ANN ARBOR, Mich.—Many biosensor technologies rely on a correlation between analyte binding and luminescence fluctuations. Unfortunately, this correlation is not always straightforward as it can be perturbed by local analyte concentration variations, the scattering properties of the sample, and absolute reading variations from instrument to instrument. An article in Nature Materials, however, suggests a possible solution.
Nanotechnologists at the University of Michigan, Athens' Ohio University, and Korea's Pusan National University have developed a sensor based on exciton-plasmon interactions between CdTe nanowires (NW) and Au nanoparticles (NP) connected by a molecular spring—a molecular spring assembly (MSA). In this case, the nanostructure is held together using PEG-antibody conjugates to form an NP-PEG-Ab-PEG-NW construct.
In the absence of antigen, the NW excitons interact with the NP plasmons to produce a specific luminescent spectrum. When antigen is present, however, the MSA is stretched, causing the exciton-plasmon interaction to be disrupted, and giving the exciton more time to diffuse along the NW. This results in the spectrum being red-shifted. The researchers found that the reaction was entirely reversible by washing the system with excess free antibody. Furthermore, using anti-streptavidin/streptavidin, spectral shifting was concentration dependent over five magnitudes. With fine tuning, the researchers are confident they can create biosensors for specific concentration ranges and with improved sensitivity.
"Compared with previous methods of sensing with Au and similar nanoparticles based predominantly on intensity variations, wavelength-shift MSAs can be particularly useful for biological applications, where the difference in the optical conditions of samples of heterogeneous tissues can be high," the authors wrote.

Randall C Willis

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