This study shows that coupling to designed plasmonic nanoparticles can modulate the electrophysiological function of proteins in living mammalian cells. Nanostar-shaped particles, that are robust to biological noise, are designed to enable near-field-coupling to plasma membrane-localized mutated Archaerhodopsin proteins in live cells. The coupled rhodopsins exhibit enhanced fluorescence and an increased response speed to membrane voltage. Incorporating this plasmonic enhancement into a Markov chain photocycle model of the Archaerhodopsin mutant QuasAr6a, shows an increased fluorescence emission rate and manipulation of the protein dynamics through a combination of photocycle transition rate enhancements. The results show an improvement in fluorescence and voltage-response dynamics of the functional QuasAr6a Archaerhodopsin mutant, beyond what has been achievable through genetic engineering. This opens up possibilities for engineering the biological functionality of proteins through plasmonics: manipulating protein photocycles could improve light sensitivity, change optogenetic applications, and lead to fluorescent biosensors with enhanced dynamics.

Direct fabrication of pure metallic nanostructures is one of the main aims of focused electron beam-induced deposition (FEBID). It was recently achieved for gold deposits by the co-injection of a water precursor and the gold precursor Au(tfac)Me₂. In this work results are reported, using the same approach, on a different gold precursor, Au(acac)Me₂, as well as the frequently used platinum precursor MeCpPtMe₃. As a water precursor MgSO₄·7H₂O was used. The purification during deposition led to a decrease of the carbon-to-gold ratio (in atom %) from 2.8 to 0.5 and a decrease of the carbon-to-platinum ratio (in atom %) from 6–7 to 0.2. The purification was done in a regular scanning electron microscope using commercially available components and chemicals, which paves the way for a broader application of direct etching-assisted FEBID to obtain pure metallic structures.

Plasmonic enhancement of fluorescence has been challenging in in vivo imaging applications. We present a study demonstrating the plasmonic enhancement of fluorescent membrane proteins within their native physiological environment using tailored metallic nanoparticles. This work highlights two schemes to influence the distance between the emitting dipoles and the enhancing nanoparticles, namely the addition of nanoparticles in the buffer solution and the incorporation in the polymer matrix at the bottom of the cells. Incorporating biological structures native to the cellular environment offers opportunities for the optimization of in vivo fluorescence imaging methods and the detection of membrane proteins.