Photocatalytic Hedgehog Particles for High Ionic Strength Environments.

High ionic strength environments can profoundly influence catalytic reactions involving charged species. However, control of selectivity and yield of heterogeneous catalytic reactions involving nano- and microscale colloids remains hypothetical because high ionic strength leads to aggregation of particle dispersions. Here we show that microscale hedgehog particles (HPs) with semiconductor nanoscale spikes display enhanced stability in solutions of monovalent/divalent salts in both aqueous and hydrophobic media. HPs enable tuning of photocatalytic reactions toward high-value products by adding concentrated inert salts to amplify local electrical fields in agreement with Derjaguin, Landau, Verwey, and Overbeek theory. After optimization of HP geometry for a model photocatalytic reaction, we show that high salt conditions increase the yield of HP-facilitated photooxidation of 2-phenoxy-1-phenylethanol to benzaldehyde and 2-phenoxyacetophenone by 6 and 35 times, respectively. Depending on salinity, electrical fields at the HP-media interface increase from 1.7 × 104 V/m to 8.5 × 107 V/m, with high fields favoring products generated via intermediate cation radicals rather than neutral species. Electron transfer rates were modulated by varying the ionic strength, which affords a convenient and hardly used reaction pathway for engineering a multitude of redox reactions including those involved in the environmental remediation of briny and salty water.

A comparison of background membrane imaging versus flow technologies for subvisible particle analysis of biologics.

A recently developed high-throughput background membrane imaging (BMI) technique, the HORIZON, was assessed for its ability to quantify subvisible particulate (SVP) generated during protein therapeutic development. The HORIZON platform method was optimized and compared to three well-characterized SVP counting techniques: light obscuration, micro-flow imaging (MFI), and FlowCam®. A head-to-head comparison was performed for precision, linearity, SVP concentration, and morphological output of BMI compared to the other three techniques using two unique enzymes under investigation. We found that dilution requirements for BMI are protein-specific, and membrane coverage is the critical instrument parameter to monitor for dilution suitability. The precision of BMI ranked similarly to all other techniques. Analysis of the same sample dilution, run in triplicate, across all four techniques indicated the BMI technique provides SVP concentrations that are comparable with the flow imaging techniques. Morphological information from BMI was generally less practical when compared with flow microscopy. The major drawback of BMI was that the current software indiscriminately clips large particles, potentially resulting in a misrepresentation of SVP size distribution. Despite this phenomenon, the concentration and size data generated corresponds well with current flow imaging techniques while decreasing time, cost, and sample requirements for SVP quantification.

Omnidispersible Hedgehog Particles with Multilayer Coatings for Multiplexed Biosensing.

Hedgehog particles (HPs) replicating the spiky geometry of pollen grains revealed surprisingly high dispersion stability regardless of whether their hydrophobicity/hydrophilicity matches that of the media or not. This property designated as omnidispersibility is attributed to the drastic reduction of van der Waals interactions between particles coated with stiff nanoscale spikes as compared to particles of the same dimensions with smooth surfaces. One may hypothesize but it remains unknown, however, whether HPs modified with polymers or nanoparticles (NPs) would retain this property. Surface modifications of the spikes will expand the functionalities of HPs, making possible their utilization as omnidispersible carriers. Here, we show that HPs carrying dense conformal coatings made by layer-by-layer (LBL/LbL) assembly maintain dispersion stability in environments of extreme polarity and ionic strength. HPs, surface-modified by multilayers of polymers and gold NPs, are capable of surface-enhanced Raman scattering (SERS) and overcome the limited colloidal stability of other SERS probes. The agglomeration resilience of HPs leads to a greater than one order of magnitude increase of SERS intensity as compared to colloids with smooth surfaces and enables simultaneous detection of several targets in complex media with high ionic strength. Omnidispersible optically active colloids open the door for rapid multiplexed SERS analysis in biological fluids and other applications.