High-precision chemical quantum sensing in flowing monodisperse microdroplets
Adrisha Sarkar, Zachary R. Jones, Madhur Parashar, Emanuel Druga, Amala Akkiraju, Sophie Conti, Pranav Krishnamoorthi, Srisai Nachuri, Parker Aman, Mohammad Hashemi, Nicholas Nunn, Marco D. Torelli, Benjamin Gilbert, Kevin R. Wilson, Olga Shenderova, Deepti Tanjore, Ashok Ajoy
Abstract
A method is presented for high-precision chemical detection that integrates quantum sensing with droplet microfluidics. Using nanodiamonds (ND) with fluorescent nitrogen-vacancy (NV) centers as quantum sensors, rapidly flowing microdroplets containing analyte molecules are analyzed. A noise-suppressed mode of optically detected magnetic resonance is enabled by pairing controllable flow with microwave control of NV electronic spins, to detect analyte-induced signals of a few hundredths of a percent of the ND fluorescence. Using this method, paramagnetic ions in droplets are detected with low limit-of-detection using small analyte volumes, with exceptional measurement stability over >10 3 s. In addition, these droplets are used as microconfinement chambers by co-encapsulating ND quantum sensors with various analytes such as single cells, suggesting wide-ranging applications including single-cell metabolomics and real-time intracellular measurements from bioreactors. Important advances are enabled by this work, including portable chemical testing devices, amplification-free chemical assays, and chemical imaging tools for probing reactions within microenvironments.