Optical density (OD) measurements are the standard approach used in microbiology for characterizing bacteria concentrations in culture media. OD is based on measuring the optical absorbance of a sample at a single wavelength, and any error will propagate through all calculations, leading to reproducibility issues. Here, we use the conventional OD technique to measure the growth rates of two different species of bacteria, Pseudomonas aeruginosa and Staphylococcus aureus. The same samples are also analyzed over the entire UV-Vis wavelength spectrum, allowing a distinctly different strategy for data analysis to be performed. Specifically, instead of only analyzing a single wavelength, a multiwavelength normalization process is implemented. When the OD method is used, the detected signal does not follow the log growth curve. In contrast, the multi-wavelength normalization process minimizes the impact of bacteria byproducts and environmental noise on the signal, thereby accurately quantifying growth rates with high fidelity at low concentrations.

Despite significant success in therapeutic development, malaria remains a widespread and deadly infectious disease in the developing world. Given the nearly 100% efficacy of current malaria therapeutics, the primary barrier to eradication is lack of early diagnosis of the infected population. However, there are multiple strains of malaria. Although significant efforts and resources have been invested in developing antibody-based diagnostic methods for Plasmodium falciparum, a rapid and easy to use screening method capable of detecting all malaria strains has not been realized. Yet, until the entire malaria-infected population receives treatment, the disease will continue to impact society. Here, we report the development of a portable, magneto-optic technology for early stage malaria diagnosis based on the detection of the malaria pigment, hemozoin. Using β-hematin, a hemozoin mimic, we demonstrate detection limits of <0.0081 μg/mL in 500 μL of whole rabbit blood with no additional reagents required. This level corresponds to <26 parasites/μL, a full order of magnitude below clinical relevance and comparable to or less than existing technologies.

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Optical cavities have successfully demonstrated the ability to detect a wide range of analytes with exquisite sensitivity. However, optimizing other parameters of the system, such as collection efficiency and specificity, have remained elusive. This presentation will discuss some of the recent work in this area, including 3D COMSOL Multiphysics models including mass transfer and binding kinetics of different cavity geometries and covalent attachment methods for a wide range of biological and synthetic moieties. A few representative experimental demonstrations will also be presented.