Nitrogen-vacancy (NV) centers in diamond are a promising platform for quantum sensing technologies. These atom-like systems hosted in the diamond crystal can be optically addressed to detect changes in magnetic field, electrochemical potential, and temperature. Furthermore, nanodiamonds (NDs) have low cytotoxicity, enabling their use in biological media. This motivates the development of a method to conjugate reporter molecules directly to the nanodiamond surface to enable site-specific quantum sensing. This past summer in Penn’s Quantum Engineering Laboratory, I was able to confirm presence and activation of nanodiamonds’ surface carboxyl groups while testing appropriate buffer systems for amine-group reactions.
The procedure for bioconjugation to the NDs’ carboxyl groups is a two-step reaction that first utilizes zero-length crosslinkers to create an amine-reactive intermediate, then reacts amine-terminated DBCO with this intermediate to create azide reactive NDs. I worked on characterizing the activation reaction that creates the amine-reactive intermediate. I performed this reaction and characterized the nanodiamonds’ activation using Fourier-transform infrared (FTIR) spectroscopy. I also performed a titration on an unreacted ND sample to confirm the presence of carboxyl groups on the ND surface.
In parallel, I studied the properties of sulfo-cyanine5 amine dye and several nanodiamond-buffer systems. Sulfo-cyanine5 amine dye can be added to the amine-reactive nanodiamonds, and its presence can be detected using UV/visible spectroscopy. Use of amine dye allows us to quantitatively confirm the efficiency of the activation step. I determined the pH dependency of the dye and conducted tests to calculate a new extinction coefficient for the dye at a neutral pH. I additionally tested the compatibility of nanodiamonds with several buffers that could raise the pH for the second step of the conjugation reaction. I used dynamic light scattering tests to determine both the size and degree of agglomeration of the nanodiamonds in various buffers.
Spending this past summer working with Dr. Bassett and his research group has enhanced my experimentation and critical thinking skills. This PURM project complemented my first-year experience at Penn, allowing me to combine the knowledge I learned in previous courses with the new information I learned each day. I will continue to work in Dr. Bassett’s lab part-time during the upcoming fall semester.