The accurate detection of low numbers of biological and chemical molecules is important for a wide range of applications including public health monitoring of viruses and bacteria, chemical threat monitoring, disease diagnostics, treatment evaluation, and food and water safety monitoring. While the detection of very low concentrations of molecules has been demonstrated, the detection of such low concentrations of molecules in dirty real-world samples such as river water, bodily fluids, polluted air, and food remains a challenge. In this work, an ultra-sensitive optical detection system will be created which is capable of simultaneous rapid molecular identification and detection. This addresses the problem of detection of low concentrations in complex mixtures. Proof-of-concept experiments will be performed to determine the accuracy of this system. In addition, we will verify our results using well-established and proven secondary techniques. This work will engage the local community through the Keep Engaging Youth in Science high school program which is run by the BIO5 Institute at the University of Arizona. At the end of the program, students present their results at a public research showcase. Engaging students early in their career on projects that can directly impact their community can help with the leaky pipeline issue, which is that not enough students are entering and staying in science and technology to satisfy the demand for such jobs in the United States. <br/> <br/>The research objective of this proposal is to create a non-imaging single molecule spectroscopic sensor. Here, a new system is proposed called FLOWERS (Frequency Locked Whispering Evanescent Resonator Spectroscopy), which incorporates dual comb frequency spectroscopy with frequency locked microtoroid optical resonators for molecular identification as well as detection. A major component of this is the use of a frequency locking feedback mechanism to track the binding events of nanoparticles and single molecules which we have previously demonstrated. The unprecedented sensitivity of this technique will be applied to spectroscopic measurements of particles as they bind. A proof-of-concept of FLOWERS will be done using rhodamine B and blue, green, orange, and dark-red fluorescent nanospheres, which have a clear spectroscopic signature. Experiments will be done at varying concentrations for all samples in order to determine the limit of detection and working range. The accuracy and noise in the spectral measurements will be characterized as a function of particle size and concentration. FLOWERS is expected to have higher precision than current state of the art spectroscopy systems enabling few false negatives. In addition, FLOWERS can potentially be more portable and automated than traditional microscopy-based single molecule spectroscopy systems.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.