Synthesis of Nanodiamond Quantum Biosensors




Assistant Professor: Electrical and Systems Engineering

Project Summary

This summer I had the opportunity to continue working in the Quantum Engineering Laboratory. Our lab studies atom-scale fluorescent defects in solids, with the aim of developing applications in quantum information processing, nanophotonics, and quantum sensing. The nitrogen-vacancy center (NV) in nanodiamond (ND) is the solid-state defect at the center of my research. The spin states of this defect in ND have the potential for in-vivo, cellular-level, site-specific biosensing. For the past year and over the course of this summer, I have worked on the synthesis of NV-based quantum biosensors.

An NV is a type of point defect in the diamond lattice in which a carbon atom in the lattice is substituted by a nitrogen atom and its closest carbon neighbor is replaced by a vacancy. As a room-temperature, optically addressable quantum spin, this defect has exceptional properties for in-vivo sensing. However, such applications first require conjugating NV-NDs to reporter molecules for probing local environments. Fluctuations in the environment trigger the reporter molecules to undergo conformational changes which are reflected in the NV-NDs’ fluorescence. Consequently, we are conjugating NV-NDs to Dibenzocyclooctyne (DBCO), a versatile cross-linker that allows for the simple attachment of different reporter molecules to the NV-ND via Cu-free click chemistry.

In order to have ultra-sensitive detection in our system (NV-ND), it is crucial for our sensor (NV) to be as close as possible to the signal (what it is detecting). Therefore, we must be able to functionalize (i.e. conjugate NDs with linker) very small (~20 nm) NV-NDs while maintaining their small size.  This means preventing agglomeration, which is a common and very well-known problem in chemical functionalization. To address this problem, we constructed a 3-step purification scheme for the functionalized NV-NDs by considering the solubility and the size of reagents involved in the conjugation reaction.

When working with nanoparticles, accurately determining size, concentration and conjugation efficiency is difficult. Our measurements required the development of a new model for scattering and absorption as a function of wavelength, and careful calibration of UV-VIS spectroscopy and dynamic light scattering (DLS) measurements. In the process of troubleshooting various inconsistencies with the procedure, I gained valuable insight into the workings of these machines and the nature of absorbance measurements. We also encountered and solved significant problems associated with measurement protocols (e.g., cuvette cleaning) and inconsistency with starting product (NDs) from the company. All in all, I have learned that bumps in research, although frustrating, are important since they lead to better understandings of the system under study.

Being part of this lab has been extremely exciting; lab members consistently motivate and inspire me to pursue post-undergrad academic goals, the research focus of the lab has given me new academic interests I can pursue in my coursework (e.g. graduate microscopy course), I have been able to apply school work to exciting, cutting edge projects. Most importantly, this lab has shown me the importance/potential of interdisciplinary research.

Synthesis of Nanodiamond Quantum Biosensors