High-Throughput Single-Entity Electrochemistry with Microelectrode Arrays.

We describe micro- and nanoelectrode array analysis with an automated version of the array microcell method (AMCM). Characterization of hundreds of electrodes, with diameters ranging from 100 nm to 2 µm, was carried out by using AMCM voltammetry and chronoamperometry. The influence of solvent evaporation on mass transport in the AMCM pipette and the resultant electrochemical response were investigated, with experimental results supported by finite element method simulations. We also describe the application of AMCM to high-throughput single-entity electrochemistry in measurements of stochastic nanoparticle impacts. Collision experiments recorded 3270 single-particle events from 671 electrodes. Data collection parameters were optimized to enable these experiments to be completed in a few hours, and the collision transient sizes were analyzed with a U-Net deep learning model. Elucidation of collision transient sizes by histograms from these experiments was enhanced due to the large sample size possible with AMCM.

Array Microcell Method (AMCM) for Serial Electroanalysis.

We describe a method for electrochemical measurement and synthesis based on the combination of a mobile micropipette and a microelectrode array, which we term the array microcell method (AMCM). AMCM has the ability to address single electrodes within a microelectrode array (MEA) and provides a simple, low-cost format to enable versatile electrochemical measurements. In AMCM, a droplet at the tip of a movable micropipette (inner diameter of 50 µm) functions as an electrochemical cell, in which the electrode area is defined by a microelectrode of the array. We also report carbon MEAs that are well suited for AMCM and are fabricated from pyrolyzed photoresist films (PPFs). PPF-MEAs with nominal electrode diameters of 5.5 µm are characterized by AMCM, standard macroscale electrochemical methods, and finite element modeling. The versatility of AMCM is demonstrated by measurement of single Pt microparticles and by electrodeposition of shapecontrolled Pt nanoparticles.

Synthesis and Characterization of Tunable, pH-Responsive Nanoparticle-Microgel Composites for Surface-Enhanced Raman Scattering Detection.

The synthesis of microgels with pH-tunable swelling leads to adjustable and pH-responsive substrates for surface-enhanced Raman scattering (SERS)-active nanoparticles (NPs). Sterically stabilized and cross-linked latexes were synthesized from random copolymers of styrene (S) and 2-vinylpyridine (2VP). The pH-dependent latex-to-microgel transition and swellability were tuned based on their hydrophobic-to-hydrophilic content established by the S/2VP ratio. The electrostatic loading of polystyrene/poly(2-vinylpyridine) microgels [PS x P2VP y (M)] with anions such as tetrachloroaurate (AuCl4 -) and borate-capped Ag NPs was quantified. The PS x P2VP y (M) can load ∼0.3 equiv of AuCl4 - and the subsequent photoreduction results in Au NP-loaded PS x P2VP y (M) with NPs located throughout the structure. Loading PS x P2VP y (M) with borate-capped Ag NPs produces PS x P2VP y (M) with NPs located on the surface of the microgels, where the Ag content is set by S/2VP. The pH-responsive SERS activity is also reported for these Ag NP-loaded microgels. Analytical enhancement factors for dissolved crystal violet are high (i.e., 109 to 1010) and are set by S/2VP. The Ag NP-loaded microgels with ∼80 wt % 2VP exhibited the most stable pH dependent response.