Laser-induced breakdown spectroscopy (LIBS) is a technique developed in the last few decades for simultaneous multi-element characterization of various materials. Multiplexed detection of analytes is particularly useful in the realm of food contaminant detection, where the contaminant can be one or a combination of adulterants. Paper-based assays are an emerging platform for food-contaminant detection. However, most paper-based assays do not perform multiplexed detection. For food contaminant outbreak prevention and remediation, rapid multiplexed detection could make a difference in response speed. This study applies LIBS to the concept of multi-analyte detection on paper-based bioassays. In the envisioned bioassay, a variety of analytes are labeled with unique lanthanides, a technique common to the well-established field of mass cytometry. The presence of single or multiple lanthanide labels indicates the presence of single or multiple types of contaminants. We aim to implement LIBS for multiplexed detection of lanthanide labels. To investigate data analysis approaches for multi-lanthanide detection, we evaluate univariate data analysis and spectral unmixing approaches on samples containing combinations of europium, dysprosium, gadolinium, praseodymium, and neodymium. We find that the intense signal generated by Eu, matrix effects, selfabsorption, and spectral overlap affect the outcome of the results. Future studies will continue the investigation to identify the most appropriate approach.
A phenotyping of bacterial colonies on agar plates using forward-scattering diffraction-pattern analysis provided promising classification of several different bacteria such as Salmonella, Vibrio, Listeria, and E. coli. Since the technique is based on forward-scattering phenomena, light transmittance of both the colony and the medium is critical to ensure quality data. However, numerous microorganisms and their growth media allow only limited light penetration and render the forward-scattering measurement a challenging task. For example, yeast, Lactobacillus, mold, and several soil bacteria form colorful and dense colonies that obstruct most of the incoming light passing through them. Moreover, blood agar, which is widely utilized in the clinical field, completely blocks the incident coherent light source used in forward scatterometry. We present a newly designed reflection scatterometer and validation of the resolving power of the instrument. The reflectance-type instrument can acquire backward elastic scatter patterns for both highly opaque media and colonies and has been tested with three different bacterial genera grown on blood agar plates. Cross-validation results show a classification rate above 90% for four genera.
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