Biosensing

Previous research highlight in biosensing:

Three-dimensional composite metallodielectric nanostructure for enhanced surface plasmon resonance sensing

Current research highlight: Ultrasensitive detection for biomedicine: Rapid detection of multi-analytes using nanoscale plasmonic devices

Nanotorch

Figure 1. a) SEM of fabricated upward nanoresonator with opening of 50nm. b) A sample uniformity plot of 5 nanotorches at different locations within the same substrate.

In the Ultrafast Nanoscale Optics group, we are utilizing nanoengineering techniques for the integration of nanoplasmonic resonators with nanofluidics in order to realize a highly sensitive and specific biomedical sensing device. By maximizing the interaction between a molecule's cross-section and the optical field, biosensing can be performed in a quick and efficient manner with high specificity and superior sensitivity, enabling diagnosis of infectious disease-causing pathogens and toxins without the need for nucleic acid amplification using PCR. While previous work required large concentrations of analytes, our goal is to develop label-free diagnostic technology and proper counter-measurements for early threat detection and recognition without the need for amplification reactions.

Previous work in optofluidics has shown that nanoparticles can be placed into nanoholes by using electroosmotic forces. Rather than manipulating particles into these holes, the resonant nanoopening can be replaced by a nanoresonator for selective placement of biomolecules onto the nanoresonator. This trapping effect allows for the molecules to be localized into the maximum optical field caused by the enhancement of the nanoresonator. This co-localization process produces a high Raman signal of the target molecule, yielding single molecular sensitivity and overcoming previous issues of label-free methods in which the optical signal was too low for molecular identification.

The ideal nanoresonator to be used for biodetection would need to have high electric field localization where the molecule interacts with the surface. A nanocrescent device, in which a spherical device is modified to have two edges with spacing in between them (Fig. 1a), has coupling of energy between nanotip and nanotip (edge to edge), nanotip and nanocavity, and nanocavity and nanobody, resulting in 3 regions in which the electric field will be amplified. Raman signature acquisitions show that the resulting enhanced Raman signal are consistent, with a reproducibility of 80% for the same substrate (Fig. 1b), meeting previous standards for commercial surface enhanced Raman scattering devices.

By integrating the nanocrescent plasmonic platform with the nanofluidic particle control chamber, an ultrasensitive, specific, and versatile device can be realized. By attenuating the current of the electric field, different particles can be measured as their interaction strength will vary, resulting in multi-analyte detection capabilities. Furthermore, the nanoplasmonic resonator enables significant field enhancement that will aid in lowering the detection limit.

References

  1. H. M. Chen, L. Pang, M. S. Gordon, Y. Fainman, Small, 7, 2750-2757 (2011).
  2. H. M. Chen, L. Pang, A. King, G. M. Hwang, Y. Fainman, submitted
  3. L. Pang, H. M. Chen, L. M. Freeman, Y. Fainman, Lab Chip, C2LC40467B, (2012).