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.

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.

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