The Ponce Group is an interdisciplinary team composed of members from both the California Institute of Technology and the NASA Jet Propulsion Laboratory that integrates microbiology, chemistry, biophotonics and engineering principles to develop chemical and biological detection schemes and corresponding analytical instrumentation. The detection of bacterial spores is a major thrust within the group. Bacterial spores, or endospores, are dormant structures primarily from Bacillus and Clostridium genera that are highly resistant to many environmental extremes. Simply put, bacterial spores are one of the toughest and most durable forms of life on earth, and are consequently fascinating subjects of investigation for a number of important applications, ranging from validation of sterilization and astrobiology to biodefense. These scientific objectives have motivated us to develop improved bacterial spore detection technologies, including a novel bacterial spore viability assay, a rapid single spore enumeration assay, and a bacterial spore monitor, dubbed the anthrax "smoke" detector.
Our group employs DPA-triggered terbium luminescence in the development of our sensors and assays for spore detection. Dipicolinic acid, or DPA, is a major constituent and unique chemical marker of bacterial spores. When released via germination or physical rupture, DPA can bind to a Tb3+ ion with high affinity to form the terbium dipicolinate binary complex [Tb(DPA)]+. This binary complex exhibits intense emission in the visible range under UV excitation, and comprises the basis of the DPA-triggered terbium photoluminescence assay used by our group and others to detect bacterial spores. To increase the sensitivity and selectivity of our endospore detection methods, we are working on the construction of a DPA-specific molecular receptor site. To this end, we are exploring several macrocyclic derivatives that bind well to Tb3+ and are capable of selecting for DPA over possible interferents. We are currently characterizing several of these ternary complexes for future modification and later use as sensors.