RESEARCH

We are interested in understanding how climate change is affecting marine and freshwater ecosystems by developing nanoscale, label-free, and in situ environmental sensors of molecular and microbial targets using materials engineering, nanophotonics, imaging, and spectroscopy. 

The oceans produce half of the oxygen in the atmosphere, cycle nearly all of the chemical elements, and store more carbon dioxide than all of the rainforests on earth combined.  Our ability to understand, predict, and respond to the changing climate requires longitudinal time-series data that correlate environmental drivers with metabolites, biomolecules, and contaminants.  Recent advances in robotic sampling, autonomous underwater vehicles (AUVs), and low-cost cameras and sensors are enabling in situ measurements of parameters like acidity, temperature, and pressure with unprecedented temporal sampling. Similar measurements of small molecules like metabolites, genes, and toxic organic contaminants are critical but remain challenging due to constraints of dominant laboratory approaches, which require large, complex, and power-intensive, and time-consuming equipment that are challenging to extend to persistent and longitudinal measurements in remote and often extreme marine environments. 

Our research group uses nanoscale control over electromagnetic radiation (light) as a sensitive, spectrally selective, and scalable toolset to address this measurement gap. Light is a powerful probe of the natural environment, where wavelengths spanning the x-ray to infrared allow us to probe and control processes spanning electronic to mechanical length scales. We develop ways to deterministically enhance, probe, and drive interactions between the incident light field and target molecules, and design compact and low-power imaging technologies. We also exploit advances in nanofabrication to work on a class of optical systems based on nanophotonics, which use subwavelength features to modulate the amplitude, phase, polarization of light in an ultrathin formfactor. We further explore how combining these optoelectronic platforms with responsive materials can transduce chemical, mechanical, and thermal signals into the optical regime, and recognize and respond to extreme conditions. We use numerical simulations to test our ideas, we fabricate and characterize our platforms using tools that we build in our lab, in the Stanford shared facilities, and at national labs, and ultimately aim to test our platforms in the field, starting in our own backyard, the Monterey Bay, at the Stanford Hopkins Marine Station. 

Broadly, just as satellite imaging has transformed our understanding of the earth’s surface, new measurements that enable in situ observation of marine environments can enable broadly transferable new technologies, reveal paths towards sustainable resource management, and open a new window of discovery into earth’s final frontier.

BIOCHEMICAL OCEANOGRAPHY: Climate change is driving fundamental shifts to microbial lifecycles in both marine and freshwater ecosystems. Photosynthetic microbes, phytoplankton, are responsible for half of the global photosynthetic carbon fixation and at least half of the world's oxygen production. However, under certain environmental conditions, phytoplankton can undergo explosive growth, forming dense harmful algal blooms (HABs) that can cover hundreds of square kilometers and can release powerful biotoxins that harm humans and wildlife, contaminate drinking water sources, and pose an economic threat to coastal economies. Understanding how environmental drivers impact plankton nutrient cycling and toxin production remains a challenge.

In collaboration with the Monterey Bay Aquarium Research Institute (MBARI) and National Centers for Coastal Ocean Science (NCCOS/NOAA), we are developing an optical sensor capable of quantitatively detecting phytoplankton toxins that can be deployed onboard autonomous underwater vehicles. By quantitatively correlating gene expression and metabolic function with environmental drivers like temperature and nutrients in real time, this work aims to probe fundamental processes in the marine biochemical cycle and to improve real time detection of harmful algal blooms (HABs) for water resource management and climate modeling.

HIGH THROUGHPUT ENVIRONMENTAL DNA (eDNA) DETECTION: Understanding biodiversity and species abundance is critical for food and economic resource management and for monitoring and maintaining ecosystem health. The oceans are the largest biological habitat in the known universe but ocean ecosystems are vast, complex, and logistically challenging to study. Quantitative measurements of environmental DNA (e-DNA), could dramatically improve our fundamental understanding of the drivers of biodiversity and environmental change.

In collaboration with the Center for Ocean Solutions and with support from the Sustainability Accelerator, we are investigating new approaches to high throughput e-DNA detection and identification using silicon nanophotonics and microfluidics. By studying diverse marine environments from the Monterey Bay to the Palau National Marine Sanctuary, we aim to improve measurements of species abundance, distribution, rare events, and early detection of invasive species. Our work was recently highlighted in the Stanford Report.

2D organic lattices and hybrid heterostructures – systems in which the electronic and optical properties can be controlled, in principle, through choice of constituent molecules – are an exceptional experimental platform to study fundamental principles of charge and energy transfer at the nanoscale. In addition to developing a mechanistic understanding of these complex dynamics, control over optoelectronic properties can enable the development of new materials for applications spanning light harvesting to water purification.

We demonstrated electronic bandstructure control in 2D organic lattices and charge and energy transfer dynamics in 2D/2D inorganic/organic heterostructure devices. We used optical spectroscopy, photoluminescence micrsocopy, AFM, high-resolution TEM, and X-ray scattering both in home-built experimental setups and at the Advanced Light Source (ALS) and the Molecular Foundry at the Lawrence Berkeley National Lab.

Electric fields mediate the transfer of information in both chemical and physical systems and are central to the ability of living systems to process and respond to environmental cues. The ability to detect and visualize electric fields in real time with high spatiotemporal resolution can open new opportunities in neuroscience, chemical sensing, and diagnostics.

Using atomically thin graphene coupled to a photonic waveguide, we developed a technique capable of imaging electric field dynamics with high spatio-temporal-voltaic resolution for the first time. We are exploring applications including real time label-free imaging of spontaneous action potentials from living systems.