To investigate whether the size of fluorescent particles affects the modulation efficiency of ultrasound-modulated fluorescence (UMF), we measured UMF and DC (direct current) signals of the fluorescence emission from four different-sized fluorescent particles: (1) three carboxylate-modified fluorescent microspheres (FM) with diameters of 20 nm, 200 nm, and 1.0 μm and (2) streptavidin-conjugated Alexa Fluor 647 with a diameter of approximately 5 nm. The UMF and DC signals were simultaneously measured using a broadband lock-in amplifier and a narrowband amplifier, respectively. The ratio of the UMF strength to the DC signal strength is defined as the modulation efficiency. This modulation efficiency was then used to evaluate the effects of fluorophore size and concentration. Results show that the modulation efficiency was improved by approximately a factor of two when the size of the fluorescent particles is increased from 5 nm to 1 μm. In addition, the linear relationship between the UMF strength and ultrasound pressure (observed in our previous study) was maintained regardless of the fluorescent particle sizes.

中文翻译：

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荧光粒径对超声调制荧光调制效率的影响。

为了研究荧光颗粒的尺寸是否影响超声调制荧光 (UMF) 的调制效率，我们测量了四种不同尺寸荧光颗粒的荧光发射的 UMF 和 DC（直流）信号：（1）三种羧酸盐修饰的荧光颗粒。直径为 20 nm、200 nm 和 1.0 μ 的荧光微球 (FM) m 和 (2) 链霉亲和素偶联的 Alexa Fluor 647，直径约为 5 nm。分别使用宽带锁定放大器和窄带放大器同时测量 UMF 和 DC 信号。UMF 强度与 DC 信号强度之比定义为调制效率。然后使用这种调制效率来评估荧光团大小和浓度的影响。结果表明，当荧光颗粒的尺寸从 5 nm 增加到 1 μm时，调制效率提高了大约两倍 。此外，无论荧光颗粒大小如何，UMF 强度和超声压力（在我们之前的研究中观察到）之间的线性关系都保持不变。