Optical tracking of nanoscale particles in microscale environments

Abstract

The trajectories of nanoscale particles through microscale environments record useful information about both the particles and the environments. Optical microscopes provide efficient access to this information through measurements of light in the far field from nanoparticles. Such measurements necessarily involve trade-offs in tracking capabilities. This article presents a measurement framework, based on information theory, that facilitates a more systematic understanding of such trade-offs to rationally design tracking systems for diverse applications. This framework includes the degrees of freedom of optical microscopes, which determine the limitations of tracking measurements in theory. In the laboratory, tracking systems are assemblies of sources and sensors, optics and stages, and nanoparticle emitters. The combined characteristics of such systems determine the limitations of tracking measurements in practice. This article reviews this tracking hardware with a focus on the essential functions of nanoparticles as optical emitters and microenvironmental probes. Within these theoretical and practical limitations, experimentalists have implemented a variety of tracking systems with different capabilities. This article reviews a selection of apparatuses and techniques for tracking multiple and single particles by tuning illumination and detection, and by using feedback and confinement to improve the measurements. Prior information is also useful in many tracking systems and measurements, which apply across a broad spectrum of science and technology. In the context of the framework and review of apparatuses and techniques, this article reviews a selection of applications, with particle diffusion serving as a prelude to tracking measurements in biological, fluid, and material systems, fabrication and assembly processes, and engineered devices. In so doing, this review identifies trends and gaps in particle tracking that might influence future research.

Three-Dimensional Localization of Single Molecules for Super-Resolution Imaging and Single-Particle Tracking

“…We are encouraged to see two recent reviews introduce ways to comprehensively describe these quantities in single-molecule microscopy, including a treatment for SR imaging(234) and one for SPT. (34) Along with theoretical comparisons, it will be necessary to characterize how robust various imaging methodologies are to common aberrations, including the effect aberrations have on precision and resolution. (235, 236) Another practical concern is the performance of different localization algorithms, and it will be necessary to continue current efforts to compare existing software packages for SR(237) and SPT(238) as our theoretical understanding and frameworks develop.…”

Particle Tracking of Microelectromechanical System Performance and Reliability

“…We also correct errors due to rotation of the torsion frame out of the imaging plane [4]. With respect to our previous work, we trade off some spatial range for temporal resolution [12], by decreasing the readout height of our complementary metaloxide-semiconductor (CMOS) camera to 128 pixels, and increasing the readout rate to 1 kHz. To maintain uncertainties at the nanometer and microradian scales, we increase both the illumination irradiance and particle diameter, boosting the mean flux of signal photons by a factor of 2.9×10 2 .…”

“…Recently, we developed a particle tracking method to resolve MEMS motion at nanometer and microradian scales. Our method is broadly applicable to diverse devices, requires only simple instrumentation, and is highly customizable within the measurement framework of optical microscopy [12]. In this Letter, we scale up the speed of our measurements by two orders of magnitude, enabling millisecond resolution and accelerating repetitive tests.…”

Transfer of motion through a microelectromechanical linkage at nanometer and microradian scales

“…Similarly, the number of fluorescent nanoparticles is largely independent of the design of the microsystem, being limited primarily by its surface area and in our experiment exceeding the number of etch holes by a factor of two. Importantly, this tracking method builds on the firm theoretical foundation of localizing point sources 37–40 , enabling novel evaluations of uncertainty and guiding future work. Experimental uncertainties are larger than the theoretical minimum uncertainties, which the number of detected photons and constellation size determine 37–39 , by a factor of only 1.3 to 1.6, indicating a nearly ideal measurement.…”