Near-Infrared Plate Reader Assay Quantifies Dopamine in Single Red Harvester Ant Brains

Thermal and desiccation stress strongly shape foraging decisions in desert ants (Pogonomyrmex barbatus), where individual workers balance food gain against the risk of water loss under hot, dry conditions. Long-term field observations suggest persistent colony-level differences in this tradeoff where risk-averse colonies reduce foraging in dry weather, while risk-tolerant colonies continue foraging, pointing to a stable neurochemical basis for collective responses to environmental stress. Prior transcriptomic and pharmacological studies implicate dopamine in desiccation-related decision-making. Here, we present a near-infrared (NIR) plate reader-based optical assay that quantifies dopamine titers in field-collected ant brain homogenates, testing whether DNA-functionalized single-walled carbon nanotube (SWCNT) dopamine nanosensors can support robust neurochemical measurements in this naturalistic model. To enable sensitive and scalable measurements from single-ant brain homogenates, we used solution-phase dopamine-responsive nanosensors and read their fluorescence in a microplate format. Dopamine-dependent modulation is quantified as a normalized intensity change (∆F/F), providing a straightforward metric compatible with frozen, homogenized biological samples. In a pilot study, we observed repeatable NIR responses from individual ant brain homogenates (∆F/F 39-51% across biological replicates), supporting the feasibility of resolving biologically meaningful differences above 10% ∆F/F. Compared with related SWCNT-based approaches that quantify endogenous dopamine primarily through microscopy-based imaging, this plate reader workflow emphasizes throughput, standardization, and accessible quantitation, making it well-suited for comparative studies across colonies and environmental conditions. Together, this platform establishes a practical route to link dopamine titers with naturally occurring variation in collective foraging strategies and provides a foundation for testing how neuromodulatory state mediates colony-level resilience to increasing thermal and desiccation stress.