Nanoplasmonic heating and sensing to reveal the dynamics of thermoresponsive polymer brushes

Abstract

Understanding of the phase transition dynamics of substrate tethered brushes of thermoresponsive poly(N-isopropylacrylamide) (pNIPAM) is important for their application as, e.g., cell substrates with spatially selective cell affinity or drug delivery systems. But characterization of the brushes phase transition time is hampered by the low amount of involved pNIPAM. Here, by the simultaneous use of time resolved nanoplasmonic heating and sensing, we are able to measure a transition time of 160±20 μs for a 30 nm thick substrate tethered brush. The plasmon-induced temperature jump can be quantitatively deduced from the measured data. Nanoplasmonic platforms as applied here could serve as local and fast probes for a variety of dynamic processes in stimuli responsive molecules or polymers.

Rapid Actuation of Thermo-Responsive Polymer Networks: Investigation of the Transition Kinetics

“…The swelling and collapse kinetics of 30 nm-thick pNIPAAm brushes on lithographically fabricated plasmonic nanoparticles demonstrated a single-exponential behavior on a time scale of 0.16 ms. 20 Contrary to this, the pNIPAAm polymer network forming a hydrogel film with a thickness of 600 nm revealed more complex swelling and collapse kinetics. The hydrogel layer responded in two phases with the faster component exhibiting a response time below 100 ms and the slower process occurring on a time scale of seconds.…”

“…Faster modulation could be achieved by more local heating approaches, for example, based on thin resistive ITO microheaters 4 or particularly via plasmonic heating. 20 Plasmonic heating relies on the optical excitation of localized surface plasmon (LSP) modes on the surface of metallic nanostructures, which originate from collective oscillations of the electron density and the associated electromagnetic field. These resonances optically probe the close vicinity of the metallic nanostructure and dissipate to heat via Ohmic losses in the metal.…”

Mapping the local particle plasmon sensitivity with a scanning probe

“…As sample we use individual gold nanoparticles fabricated by electron beam lithography on glass substrates. 28 The quasi-identical nanoparticles have an elliptical footprint with lateral dimensions of 140 ± 5 nm × 120 ± 5 nm and a height of 25 ± 3 nm. When excited along the long particle axis the LSPR peak is at 705 nm ( Fig.…”

Influence of the CTAB surfactant layer on optical properties of single metallic nanospheres

“…The LSPR spectral peak position and its form strongly depend on many factors such as the nanoparticle size, shape, material, as well as on the refractive index of surrounding medium. The LSPR spectral tunability and high electric field enhancement near the metallic nanoparticles open a wide area of applications in bio or chemical sensing, surface enhanced spectroscopies, lasing, local thermal treatment, color generation and etc [1][2][3][4][5][6][7][8][9][10].…”