Photoinduced enhanced Raman spectroscopy from a lithium niobate on insulator (LNOI)-silver nanoparticle template is demonstrated both by irradiating the template with 254 nm ultraviolet (UV) light before adding an analyte and before placing the substrate in the Raman system (substrate irradiation) and by irradiating the sample in the Raman system after adding the molecule (sample irradiation). The photoinduced enhancement enables up to an ∼sevenfold increase of the surface-enhanced Raman scattering signal strength of an analyte following substrate irradiation, whereas an ∼threefold enhancement above the surface-enhanced signal is obtained for sample irradiation. The photoinduced enhancement relaxes over the course of ∼10 h for a substrate irradiation duration of 150 min before returning to initial signal levels. The increase in Raman scattering intensity following UV irradiation is attributed to photoinduced charge transfer from the LNOI template to the analyte. New Raman bands are observed following UV irradiation, the appearance of which is suggestive of a photocatalytic reaction and highlight the potential of LNOI as a photoactive surface-enhanced Raman spectroscopy substrate.
In vitro devices that combine chemotactic and physical cues are needed for understanding how cells integrate different stimuli. We explored the suitability of lithium niobate (LiNbO3), a transparent ferroelectric material that can be patterned with electrical charge domains and micro/nanotopography, as a neural substrate. On flat LiNbO3 z-surfaces with periodically alternating charge domains, cortical axons are partially aligned with domain boundaries. On submicron-deep etched trenches, neurites are aligned with the edges of the topographical features. Finally, we bonded a bicompartmental microfluidic chip to LiNbO3 surfaces patterned by etching, to create isolated axon microenvironments with predefined topographical cues. LiNbO3 is shown to be an emerging neuron culture substrate with tunable electrical and topographical properties that can be integrated with microfluidic devices, suitable for studying axon growth and guidance mechanisms under combined topographical/chemical stimuli.
An important aspect of optimizing
micro- and optofluidic devices
for lab-on-a-chip systems is the ability to engineer materials properties
including surface structure and charge to control wettability. Biocompatible
ferroelectric lithium niobate (LN), which is well-known for acoustic
and nonlinear optical applications, has recently found potential micro-
and optofluidic applications. However, the tunable wettability of
such substrates has yet to be explored in detail. Here, we show that
the contact angle of LN substrates can be reproducibly tailored between
∼7° and ∼121° by controlling the surface topography
and chemistry at the nano- and micrometer scale via ferroelectric
domain and polarization engineering and polarization-directed photoassisted
deposition of metallic nanostructures.
We examine here a series of meso-phenyl porphyrin micro- and nanostructures. Optical absorption and emission spectroscopy imaging and atomic force microscopy are used to investigate the effect of peripheral groups in nano- and microstructures of 5,10,15,20-tetraphenylporphyrin (H2TPP) compared to three other phenylporphyrins, i.e. 5,10,15-triphenylporphyrin (H2-Tri-PP), 5,10-diphenylporphyrin (H25,10-BPP) and 5,15-diphenylporphyrin (H25,15-BPP) molecules. We show that nanospheres and nanorods are formed, the occurrence and properties of which are influenced by the number and position of the phenyl substituents.
Single-molecule
detection by surface-enhanced Raman scattering
(SERS) is a powerful spectroscopic technique that is of interest for
the sensor development field. An important aspect of optimizing the
materials used in SERS-based sensors is the ability to have a high
density of “hot spots” that enhance the SERS sensitivity
to the single-molecule level. Photodeposition of gold (Au) nanoparticles
through electric-field-directed self-assembly on a periodically proton-exchanged
lithium niobate (PPELN) substrate provides conditions to form well-ordered
microscale features consisting of closely packed Au nanoparticles.
The resulting Au nanoparticle microstructure arrays (microarrays)
are plasmon-active and support nonresonant single-molecule SERS at
ultralow concentrations (<10
–9
–10
–13
M) with excitation power densities <1 ×
10
–3
W cm
–2
using wide-field imaging.
The microarrays offer excellent SERS reproducibility, with an intensity
variation of <7.5% across the substrate. As most biomarkers and
molecules do not support resonance enhancement, this work demonstrates
that PPELN is a suitable template for high-sensitivity, nonresonant
sensing applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.