Intellectual Merits: The objective of this CAREER proposal is to demonstrate high sensitivity detection of biomolecules on a silicon platform for the development of reliable, portable, and cost-effective biosensors. The demonstration of such a biosensor using silicon-compatible processing techniques could revolutionize medical diagnostics. In this work, the optical properties of porous silicon are utilized for the detection of biomolecules. The pores not only provide a means of improving selectivity by filtering unwanted species, but their large surface area allows the attachment of more biomolecules than is attainable on planar substrates. The design of the porous silicon sensor as a waveguide enables the majority of the electric field to interact with the biomolecules, resulting in highly sensitive detection. When biomolecules are captured in the waveguide, the refractive index change can be measured by a shift in the waveguide resonance angle. Fundamental studies on how electric field-biomolecule interaction relates to biosensor performance will lead to advanced biosensing technology. Accurate predictions of how increased surface area from the use of porous media can enhance device performance will be valuable across several fields of research from biosensors to solar cells and optical switches.
Broader Impacts: There is a strong demand for the development of a reliable, sensitive, portable biosensor that is cost-effective for applications in medical diagnostics, environmental monitoring, and homeland security. The proposed research opens the door to breakthrough technology for biomolecular sensing that can tap into the multibillion dollar biotechnology industry. The educational goals of this program include (1) developing a new course highlighting optical properties of nanomaterials; (2) offering summer research opportunities for minority students; (3) participation in hands-on outreach activities at Nashville area schools; and (4) working to sustain interest in physics and engineering for graduate and undergraduate women in these fields.
Intellectual Merit: This CAREER program investigated the design and characterization of porous silicon optical structures for the effective detection of chemical and biological molecules. Analysis was performed to understand how the interaction of light with the porous silicon structures can be maximized to improve the detection sensitivity of the structures as chemical and biological sensors. A variety of chemical functionalization approaches were investigated to understand the size limitations of infiltrating and attaching molecules in high aspect ratio nanoscale pores. Porous silicon waveguide sensors were demonstrated to improve the detection sensitivity of comparable planar silicon waveguide sensors by one order of magnitude, largely due to the increased internal surface area available to capture and detect the molecules of interest. A microfluidics system was integrated with the porous silicon waveguide sensor to explore the molecular binding kinetics of the system. Although the desired molecules could be detected by the sensors within the first minute of exposure to the sensor, the binding kinetics were found to be slower compared to planar silicon waveguide sensors due to the additional number of binding sites available for the molecules. Two design modifications to the porous silicon sensor were explored. First, a porous silicon Bloch surface wave sensor was demonstrated that allowed light to be concentrated both within the porous silicon structure, similar to the porous silicon waveguide sensor, but also at the top surface of the porous silicon. This new design allowed for the simultaneous detection of large surface-bound molecules that were too large to enter the pores and small molecules that could take advantage of binding within the large internal surface area of the pores. Second, a porous silicon ring waveguide sensor was demonstrated that enabled even larger interaction between light and molecules of interest inside the porous silicon material. An additional one order of magnitude detection sensitivity improvement was achieved with this structure. Throughout the program, nucleic acid molecules with direct relevance to genomic studies were utilized as test molecules for the porous silicon sensors. Broader Impact: The results of this CAREER program may lead to development of reliable, sensitive, portable chemical and biological sensors for applications spanning medical diagnostics, environmental monitoring, and homeland security. Moreover, insights into how to effectively load nanoscale void spaces with chemical and biological molecules are likely to be leveraged in emerging technologies within the energy sector, including solar cells, fuel cells, and supercapacitors. A total of 7 graduate students, 8 undergraduate students, and 1 high school teacher participated in this research effort, including 7 underrepresented minority students in STEM fields. The participating students are entering the workforce well-qualified to conduct independent or team research at the cutting-edge of modern technology. Moreover, undergraduate and graduate students enrolled in a new course taught by the principal investigator of this program were exposed to emerging science at the intersection of nanotechnology, physics, materials science, and chemistry, and are hence better prepared to contribute to the development of new technologies that, more than ever, now leverage aspects from multiple disciplines. More than 10 STEM outreach activities were conducted to middle school and high school students, and additional activities targeted to the broader Nashville community were conducted at the Nashville Adventure Science Center. Participation of a high school teacher from Middle Tennessee led to the creation of a lesson plan entitled, "Tell me the odds (of cancer)" that was written for AP level Physics students but could be modified for conceptual physics classes. The lesson, which incorporates hands-on activities with porous silicon DNA sensors, challenges the students to apply basic physics concepts to study cancer risk analysis.
