In health and environmental research, it is often necessary to quantify the concentrations of single (bio) nanoparticles present at very low concentrations. Suitable quantification approaches that rely on counting and tracking of single fluorescently labelled (bio) nanoparticles are often challenging since fluorophore self-quenching limits the maximum particle brightness. Here we study how the number of labels per nanoparticle influences the total brightness of fluorescently labelled cowpea chlorotic mottle virus (CCMV). We analyze in detail the photophysical interplay between the fluorophores on the virus particles. We deduce that the formation of dark aggregates and energy transfer towards these aggregates limits the total particle brightness that can be achieved. We show that by carefully selecting the number of fluorescent labels per CCMV, and thus minimizing the negative effects on particle brightness, it is possible to quantify fluorescently labelled CCMV concentrations down to fM concentrations in single particle counting experiments.

在健康和环境研究中，通常需要量化以极低浓度存在的单个（生物）纳米颗粒的浓度。依赖于单个荧光标记（生物）纳米粒子的计数和跟踪的合适量化方法通常具有挑战性，因为荧光团自猝灭限制了最大粒子亮度。在这里，我们研究了每个纳米颗粒的标记数量如何影响荧光标记的豇豆褪绿斑驳病毒 (CCMV) 的总亮度。我们详细分析了病毒颗粒上荧光团之间的光物理相互作用。我们推断暗聚集体的形成和向这些聚集体的能量转移限制了可以实现的总粒子亮度。我们表明，通过仔细选择每个 CCMV 的荧光标记数量，