Water-dispersible three-dimensional LC-nanoresonators

Abstract

Nanolithography techniques enable the fabrication of complex nanodevices that can be used for biosensing purposes. However, these devices are normally supported by a substrate and their use is limited to in vitro applications. Following a top-down procedure, we designed and fabricated composite inductance-capacitance (LC) nanoresonators that can be detached from their substrate and dispersed in water. The multimaterial composition of these resonators makes it possible to differentially functionalize different parts of the device to obtain stable aqueous suspensions and multi-sensing capabilities. For the first time, we demonstrate detection of these devices in an aqueous environment, and we show that they can be sensitized to their local environment and to chemical binding of specific molecular moieties. The possibility to optically probe the nanoresonator resonance in liquid dispersions paves the way to a variety of new applications, including injection into living organisms for in vivo sensing and imaging.

Figure 1. Design and LC behaviour.

(A) Design of a three-dimensional nanoresonator and its schematization as nanocircuit (B–C) Simulations with Comsol 4.2: z-component of the electic and norm of the magnetic fields (colour plot) demostrate the LC-behaviour at NIR wavelengths. The arrows represent the direction and sign of electric and magnetic field.

Figure 2. Nanoresonators and their characterization.

(A) SEM-image of the nanoresonators disposed in array (B) SEM-image of nanoresonators pulled off the substrate and randomly oriented (C) Transmission spectrum of nanoresonators disposed in array for different polarizations.

Figure 3. Nanoresonators in a microfluidic chip.

(A) Microfluidic chip with gold markers (B) Shift of the resonance for three liquids with different refractive indexes injected into the chamber (C) Transmission spectra resolved in time during cysteamine-binding (D) Study of Cysteamine-binding kinetics. The error bar is taken as half the acquisition time of every single measurement.

Figure 4. Sensing with suspended nanoresonators.

Spectra of nanoresonators in water and DMSO.

Figure 5. Nanofabrication process and chemical functionalization.

(a) top-down approach to define the nanostructure (b) selective wet etching to pull the nanoresonators off the substrate (c) chemical functionalization to suspend the nanoresonators in watery environment.