Max Fei

We demonstrate the fabrication of novel functional gel coatings with randomized physical and chemical patterns that enable dual encoding ability to realize unclonable optical tags. This design is based on swelling-mediated massive reconstruction of an ultrathin responsive gelatinous polymer film uniformly adsorbed with plasmonic nanostructures into a randomized network of interacting folds, resulting in bright electromagnetic hotspots within the folds. We reveal a strong correlation between the… Show more

We demonstrate the fabrication of novel functional gel coatings with randomized physical and chemical patterns that enable dual encoding ability to realize unclonable optical tags. This design is based on swelling-mediated massive reconstruction of an ultrathin responsive gelatinous polymer film uniformly adsorbed with plasmonic nanostructures into a randomized network of interacting folds, resulting in bright electromagnetic hotspots within the folds. We reveal a strong correlation between the topology and near-field electromagnetic field enhancement due to the intimate contact between two plasmonic surfaces within the folds, each of them representing a unique combination of local topography and chemical distribution caused by the formation of electromagnetic hotspots. Because of the efficient trapping of the Raman reporters within the uniquely distributed electromagnetic hotspots, the surface enhanced Raman scattering enhancement from the morphed plasmonic gel was found to be nearly 40 times higher compared to that from the pristine plasmonic gel. Harnessing the nondeterministic nature of the folds, the folded plasmonic gel can be employed as a multidimensional (with dual topo-chemical encoding) optical taggant for prospective anticounterfeiting applications. Such novel optical tags based on the spontaneous folding process are virtually impossible to replicate because of the combination of nondeterministic physical patterns and chemical encoding. Show less

Surface-enhanced Raman scattering (SERS) tags that serve as exogenous contrast agents for SERS-based bioimaging are comprised of size- and shape-controlled plasmonic nanostructures. For maximum SERS activity and image contrast, the localized surface plasmon resonance (LSPR) wavelength of SERS tags based on individual nanostructures must match with the excitation wavelength (typically in the near-infrared (NIR) therapeutic window, i.e., 650–900 nm). However, under the resonant excitation, these… Show more

Surface-enhanced Raman scattering (SERS) tags that serve as exogenous contrast agents for SERS-based bioimaging are comprised of size- and shape-controlled plasmonic nanostructures. For maximum SERS activity and image contrast, the localized surface plasmon resonance (LSPR) wavelength of SERS tags based on individual nanostructures must match with the excitation wavelength (typically in the near-infrared (NIR) therapeutic window, i.e., 650–900 nm). However, under the resonant excitation, these SERS tags typically exhibit very high photothermal conversion efficiency, resulting in excessive heat that can perturb or even damage the biological species being imaged. Here, we demonstrate bioenabled synthesis of a novel class of ultrabright SERS probes with built-in and accessible electromagnetic hotspots formed by densely packed satellite nanoparticles grown on a plasmonic core. Through the rational choice of the shape of the core, the LSPR wavelength of Au superstructures can be tuned to be either off- or on-resonant with the NIR excitation without sacrificing their high SERS activity. Consequently, the photothermal efficiency of these ultrabright SERS tags can be tuned to realize either contrast agents with minimal heating and perturbation or multifunctional theranostic agents that can image and photothermally kill the targeted cells. Show less

The bio-enabled synthesis of a novel class of surface enhanced Raman scattering probes is presented for functional imaging with built-in and accessible electromagnetic hotspots formed between densely packed satellites grown on a plasmonic core. The superstructures serve as nanoscale sensors to spatiotemporally map intravesicular pH changes along endocytic pathways inside live cells.

The synthesis of plasmonic nanorattles with accessible electromagnetic hotspots that facilitate highly sensitive detection of chemical analytes using surface enhanced Raman scattering (SERS) is demonstrated. Raman spectra obtained from individual nanorattles demonstrate the significantly higher SERS activity compared to solid plasmonic nanostructures.

The combination of stimuli-responsive materials with localized surface plasmon resonance nanotransducers provides new leverages in hot spot-based nanosensing. We introduce a simple and effective biodetection method based on the hydro-responsive property of (3-aminopropyl)-triethoxysilane (APTES). Gold nanoparticles were adsorbed onto hydro-responsive APTES thin film. The exposure of the film surface to an aqueous solution results in opening inter-particle gaps, allowing analyte binding. A… Show more

The combination of stimuli-responsive materials with localized surface plasmon resonance nanotransducers provides new leverages in hot spot-based nanosensing. We introduce a simple and effective biodetection method based on the hydro-responsive property of (3-aminopropyl)-triethoxysilane (APTES). Gold nanoparticles were adsorbed onto hydro-responsive APTES thin film. The exposure of the film surface to an aqueous solution results in opening inter-particle gaps, allowing analyte binding. A subsequent drying of the sensor surface closes the gap by bringing the nanoparticles to the initial position, thereby trapping the analyte in the most sensitive regions (electromagnetic hot spots). In this reversible configuration, the generation and tuning of the hot spots are independent from both the presence of the analyte and the functionalization of the nanoparticles, which yields highly resolved coupled plasmon bands and provide a general and flexible nanosensing modality. Furthermore, the intensity of the hot spots can be easily and reversibly tuned to obtain picomolar sensitivity. Show less

In this work, we demonstrate that plasmonic nanostructures can be employed as nanoscale transducers to monitor the growth and phase transitions in ultrathin polymer films. In particular, gold nanorods with high refractive index sensitivity (~150 nm/refractive index unit (RIU)) were employed to probe the growth and swelling of polyelectrolyte multilayers (PEM). By comparing the wavelength shift and extinction intensity increase of the localized surface plasmon resonance (LSPR) of the gold… Show more

In this work, we demonstrate that plasmonic nanostructures can be employed as nanoscale transducers to monitor the growth and phase transitions in ultrathin polymer films. In particular, gold nanorods with high refractive index sensitivity (~150 nm/refractive index unit (RIU)) were employed to probe the growth and swelling of polyelectrolyte multilayers (PEM). By comparing the wavelength shift and extinction intensity increase of the localized surface plasmon resonance (LSPR) of the gold nanorods coated with PEM in air and water, the swelling of PEM was estimated to be 26% ± 6%. The swelling was quantitatively confirmed with independent thickness measurement of PEM in dry and swollen states using AFM. The deployment of shape-controlled metal nanostructures with high refractive index sensitivity represents a novel and facile approach for monitoring the phase transition in polymers with nanoscale resolution. Show less