Research Interests

of the Sailor Group at UC San Diego

Our research focuses on silicon nanotechnology, with emphasis on drug delivery materials, in vivo and in vitro imaging with magnetic and photoluminescent nanoparticles, photonic crystals, nanophase silicon-based anode materials, remote chemical sensing, biosensing, catalysis, and thermoelectric materials. Our group is expert in the chemistry, electrochemistry, and optical properties of silicon-based nanomaterial systems. The major research themes are given below.

Porous Silicon Nanoparticles for Delivery of Biologics

We are developing approaches to deliver protein and nucleic acid-based therapeutics for treatment of infectious diseases, diseases of the retina, and cancer. We developed a new chemistry to load oligonucleotides and other negatively charged payloads into porous Si nanoparticles, based on precipitation of endogenous silicate with calcium or magnesium ions (Adv. Mater. 2016, 28, 7962). This achieved the highest mass loading of nucleic acid for any nanoparticle system to date, and it is the enabling feature of the porous Si nanoparticle systems we have been developing for treatment of cancer, inflammatory diseases, and infections. This included the first example of siRNA used to reprogram the immune system's macrophages to cure a lethal bacterial infection (Nat. Commun. 2018, 9, 1969). This work has also made a commercial impact as inventions related to these porous Si particles are being translated to the clinic).

Non-Toxic, Biocompatible Silicon “Quantum Dots” as Imaging Agents

We demonstrated the first in vivo use of luminescent porous Si as an imaging agent (Nature Mater. 2009, 8, 331). Our most highly cited paper to date (> 1700 citations), in 2012 it was highlighted by the editors of Nature Materials as one of the “Landmark Papers” published by the Journal in the previous 10 years. We provided the first example of time-gated imaging in live animals using porous Si nanoparticles (Nat. Commun. 2013, 4, 2326), where we showed that interference from tissue autofluorescence and other competing fluorophores can be reduced by more than 100-fold. This work has played a major role in the current explosion of interest in silicon quantum dots as in vitro and in vivo probes. Our work here is enabled by various aqueous-based surface oxidation chemistries being developed to generate highly emissive, but biodegradable Si-SiO2 core-shell nanomaterials (ACS Nano 2015, 9, 6233).

Microparticles of Porous Silicon

Since their discovery in 1992 (Science 1992, 255, 66), particles made from porous silicon have been of interest to a wide range of research disciplines. We deploy micron-scale photonic crystals of porous Si (so-called “Smart Dust” Proc. Nat. Acad. Sci. 2003, 100, 10607), in applications such as environmental and remote sensing. The fundamental electrochemistry involved in anodization of silicon allows the generation of complex nanostructures. The substantial impact of the work includes commercial development of the “spectral barcodes” concept as non-toxic tags for pharmaceuticals and durable goods (TruTags, inc).

Chemical Sensors and Biosensors using Porous Silicon Optical Films

Our group provided the first demonstrations of chemical and biological sensing using optical interferometry from porous silicon (J. Electrochem. Soc. 1993, 140, 3492; Science 1997, 278, 840). Our current biosensing strategies use the RIFTS (Reflective Interferometric Fourier Transform Spectroscopy) method (J. Am. Chem. Soc. 2006, 128, 4250), which has been widely adopted in the chemical and biochemical sensing communities, and SLIM (Spectroscopic Liquid Infiltration Method), commonly used to quantify thickness and porosity of porous optical films (Adv. Funct. Mater. 2007, 17, 1153).

Surface Chemistry of Silicon Nanomaterials

In collaboration with Barry Arkles and his team at Gelest, our group demonstrated the first catalyst-free dehydrocoupling reaction to modify porous Si surfaces (Angew. Chem. 2016, 128, 6533), which has been very useful in stabilizing chemical sensors based on the material because it proceeds at substantially lower temperatures and is less susceptible to water impurities than the more commonly employed hydrosilylation reaction. We also provided the first example of the use of heterocyclic silanes as simple, rapid, and one-pot reagents to modify silicon surfaces--we are developing these reagents as an alternative to the ubiquitous tri- or mono-alkoxysilane coupling reagents currently used to modify hydroxy-terminated surfaces (J. Am. Chem. Soc. 2016, 138, 15106).

Summer School for Silicon Nanotechnology (SSSiN)

All trainees in the Sailor Group begin with the SSSiN, an immersive six-week workshop on the preparation, characterization, and applications of porous silicon-based nanomaterials. This provides the basic training of incoming graduate students, undergraduates, visiting scholars, and high school students.

Although the scope of our work at the University is limited to basic research into the fundamental properties of materials, many of the concepts developed in our labs have been translated to products and processes in the commercial world. Any commercial products and processes that emerge from our fundamental discoveries are outside the course and scope of our University-related employment; however, we actively encourage transition of technologies to the commercial sector with the assistance of UCSD’s Office of Innovation and Commercialization