posted on 2021-11-23, 19:35authored byAsma Akther, Ella P. Walsh, Philipp Reineck, Brant C. Gibson, Takeshi Ohshima, Hiroshi Abe, Gawain McColl, Nicole L. Jenkins, Liam T. Hall, David A. Simpson, Amgad R. Rezk, Leslie Y. Yeo
Diamond nitrogen-vacancy (NV) centers
constitute a promising class
of quantum nanosensors owing to the unique magneto-optic properties
associated with their spin states. The large surface area and photostability
of diamond nanoparticles, together with their relatively low synthesis
costs, make them a suitable platform for the detection of biologically
relevant quantities such as paramagnetic ions and molecules in solution.
Nevertheless, their sensing performance in solution is often hampered
by poor signal-to-noise ratios and long acquisition times due to distribution
inhomogeneities throughout the analyte sample. By concentrating the
diamond nanoparticles through an intense microcentrifugation effect
in an acoustomicrofluidic device, we show that the resultant dense
NV ensembles within the diamond nanoparticles give rise to an order-of-magnitude
improvement in the measured acquisition time. The ability to concentrate
nanoparticles under surface acoustic wave (SAW) microcentrifugation
in a sessile droplet is, in itself, surprising given the well-documented
challenge of achieving such an effect for particles below 1 μm
in dimension. In addition to a demonstration of their sensing performance,
we thus reveal in this work that the reason why the diamond nanoparticles
readily concentrate under the SAW-driven recirculatory flow can be
attributed to their considerably higher density and hence larger acoustic
contrast compared to those for typical particles and cells for which
the SAW microcentrifugation flow has been shown to date.