Tricarb 2500tr liquid scintillation counter

The Local Lymph Node Assay (LLNA) was performed in accordance with previously-established standardized protocols (Basketter et al. 2002 (link)). Accordingly, mice (n = 8 per group) were exposed topically to vehicle control (50% DMSO in distilled, deionized water), increasing concentrations of Au or AuNP, or positive control (10% AuCl₃) on the dorsal sides of both ears (25 μL per ear) for three consecutive days (days 1, 2, and 3) (Figure 1). Following two days of rest, on day 6, mice were injected intravenously via the lateral tail vein with 20 μCi [³H]-thymidine (Dupont NEN, specific activity 2 Ci/mmol). Five hours after the [³H]-thymidine injection, mice were euthanized via CO₂ asphyxiation and the left and right auricular lymph nodes (ALN) were excised from each mouse and pooled. Single-cell suspensions were prepared, and following overnight incubation in 5% trichloroacetic acid (TCA), samples were analyzed using a Packard Tri-Carb 2500TR liquid scintillation counter. Stimulation indices (SI) were calculated by dividing the mean disintegrations per minute (DPM) per test group by the mean DPM for the vehicle control group.