Dr. Wei-Chuan Shih at the University of Houston was awarded an RFP-II grant at $740,268 to conduct the RFP-II project titled, “Novel Sensor System for the Early Detection and Monitoring of Offshore Oil Spills”. The project consisted of 1 institution (University of Houston), 1 principal investigator (Shih), 2 co-PIs (Glennie, Han), 1 post- doc (Santos), 6 graduate students (Arnob, Li, Liu, Lu, Qi, Wang), and participation by several research technicians and graduate students.
Despite the pressing needs, effective detection and quantification of oil spills has not become a technological reality. Current detection methods employ manual identification using routine helicopter surveys, which are severely limited in their efficiency, by weather conditions, cost, and safety considerations. The Gulf of Mexico (GOM) requires an efficient, reliable, automated and cost effective method of monitoring for spills, especially given that 90% of the more than 6000 platforms in the GOM are unmanned and unpowered. To this end, this project aims to develop an innovative sensor system to quantify oil film thickness using multispectral infrared (IR) imaging and computational reconstruction. Such a system can aid human observers in making objective and accurate decisions, or alternatively be installed on the platform as an automated and permanent sensor for 24/7 operations, replacing or greatly reducing the frequency of current helicopter surveys.
The team will exploit the novel ultrasensitive detection mechanisms in the spectral and thickness modulations of oil films recently modeled and experimentally confirmed by the PI. In addition, the team will design and fabricate a novel class of gold nanoparticles, dubbed nanoporous gold arrays, for enhancing the signal from surface hydrocarbon species. Several optical sensing mechanisms are envisioned to be exploited such as thermal, infrared absorption, Raman scattering, fluorescence, and refractive index sensing. These novel contrast mechanisms will enable the measurement of oil film thickness with 24/7 detectability. The proposed sensors are envisioned to be integrated with multispectral imaging with a computational core to exploit the benefits of data sparsity. The system is potentially an extremely cost-effective permanent sensor installed on platforms for offshore oil spill detection. Alternatively, the proposed system could be integrated with a small unmanned aerial vehicle (UAV) for task-specific missions. Ultimately, many sensor systems can be installed on multiple platforms, forming a sensor network for oil spill trajectory monitoring and environmental forensics.
Dr. Shih’s research resulted in 5 peer-reviewed publications and 5 datasets being submitted to the GoMRI Information and Data Cooperative (GRIIDC), which are/will be available to the public. Significant outcomes of his research, according to GoMRI Research Theme 4 are highlighted below.
In summary, this project demonstrated shape and size-controlled monolithic NPG disks as a new type of plasmonic nanoparticle in both substrate-bound and non-aggregating colloidal formats. NPG disks feature large specific surface area due to their internal nanoporous network. NPG disks also contain numerous plasmonic hot-spots throughout the internal volume, which has enabled the demonstration of the high LSPR sensitivity to ambient index changes. Putting NPG disks into the context of existing repertoire of gold nanoparticles, which permits tunability by varying parameters in design dimensions such as material composition, particle size, shape (e.g., sphere, rod, cube, triangle, and cage) and configuration (core-shell), our work strongly advocates porosity as yet another potential design dimension for plasmonic engineering. In addition to its excellent plasmonic properties, the gold material permits facile binding of a wide range of thiolated molecular and biomolecular species through the Au-S bond. The synergy of large specific surface area, high-density hot spots, and tunable plasmonics would profoundly impact applications where plasmonic nanoparticles and non-plasmonic mesoporous nanoparticles are currently employed, e.g., in in-vitro and in-vivo biosensing, molecular imaging, photothermal contrast agents, and molecular cargos.
In this study, the NPG disk array on glass was demonstrated as an excellent substrate for index and surface-enhanced near-infrared absorption (SENIRA) sensing across the broad 1000-2500 nm range required for detection of molecular overtones for C-H and O-H functional groups. The NPG disk array substrate reported herein provide a new, multifunctional platform for chemical sensing by NIR absorption at different sample volumes: from monolayer and multilayer thin films to bulk amounts. The LSPR shift and SENIRA characterization of patterned NPG nanoparticles provides an insight for the detailed correlation between near-field properties and spectroscopic enhancement which will pave for highly customizable plasmonic geometries for NPG nanoparticles to meet the requirements for sensitive molecular detection in the NIR wavelengths.
We have continued to make progress in nanosensor fabrication for hydrocarbon molecular sensing and developing a near-infrared hyperspectral imaging sensor. The nanoporous gold array chip (NPGAC) developed previously has become a highly versatile “surface” for many different applications. In addition to hydrocarbon sensing, NPGAC has been demonstrated to be useful in general chemical/biological sensing of disease biomarkers and other environmental pollutant/toxin/carcinogen. Although these sensing targets are not immediately relevant to the project, we are nevertheless extremely excited about their broadly applicability. This was emphasized during a phone discussion with Mr. Charles Wilson. On the second area, the NIR hyperspectral imaging sensor has been employed in acquiring experimental spectra from various hydrocarbon molecules deposited on NPGAC, which exhibits strong near-field enhancement. In other words, the NIR absorption spectrum of hydrocarbon molecules become highly enhanced due to the excitation of localized surface plasmon resonance on NPGAC. These results were documented in an article published in ACS Nano Letters, a prestigious journal with an impact factor ~14. A new manuscript describing the instrument titled “Hyperspectral near-infrared imaging sensor of hydrocarbon molecules using a digital micro-mirror device and a linear detector array” has been under preparation and slight setback was experienced because of the departure of a postdoc associate who was the lead author. The PI and Co-PI are working closely with another PhD student to finish the rest of the work and we look forward to submit this manuscript for review in 2017.