Selectivity is often a major obstacle for localized surface plasmon resonance-based biosensing in complex biological solutions. An additional degree of selectivity can be achieved through the incorporation of shape complementarity on the nanoparticle surface. Here, we report the versatile fabrication of substrate-bound Au-Ag nanobowl arrays through the galvanic ion replacement of silver nanodisk arrays. Both localized surface plasmon resonance (LSPR) and surface enhanced Raman spectroscopy (SERS) were carried out to detect the binding of analytes of varying size to the nanobowl arrays. Large increases in the LSPR and SERS response were measured for analytes that were small enough to enter the nanobowls, compared to those too large to come into contact with the interior of the nanobowls. This size-selective sensing should prove useful in both size determination and differentiation of large analytes in biological solutions, such as viruses, fungi, and bacterial cells.
To clarify the cis–trans
isomerization mechanism of simple
alkenes on the triplet excited state surface, the photochemistry of
acyclic and cyclic vinyl ketones with a p-methoxyacetophenone
moiety as a built-in triplet sensitizer (1 and 2, respectively) was compared. When irradiated, ketone 1 produces its cis-isomer, whereas ketone 2 does
not yield any photoproducts. Laser flash photolysis of ketone 1 yields a transient spectrum with λmax ∼
400 nm (τ ∼ 125 ns). This transient is assigned to the
first triplet excited state (T1) of 1, which
presumably decays to form a triplet biradical (1BR) that
is shorter lived than the triplet ketone. In comparison, laser flash
photolysis of 2 reveals two transients (τ ∼
20 and 440 ns), which are assigned to T1 of 2 and triplet biradical 2BR, respectively. Density functional
theory calculations support the characterization of the triplet excited
states and the biradical intermediates formed upon irradiation of
ketones 1 and 2 and allow a comparison of
the physical properties of the biradical intermediates. As the biradical
centers in 2BR are stabilized by conjugation, 2BR is more rigid than 1BR. Therefore, the longer lifetime
of 2BR can be attributed to less-efficient intersystem
crossing to the ground state.
Nanoelectrode arrays consisting of vertically aligned carbon nanofibers were prepared through plasma enhanced chemical vapor deposition and patterned using hole‐mask colloidal lithography (HCL), a simple fabrication method employed as a cost‐effective patterning alternative to the conventional electron beam lithography. The density of the carbon nanofibers was easily altered by changing the concentration of the polystyrene spheres employed in HCL. Cyclic voltammetry and chronoamperometry were used to electrochemically characterize the arrays of different density. Results indicate that the density of the carbon nanofibers leads to differences in the macro/micro electroactive surface areas.
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