1900737 (1 of 26) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim REVIEW www.small-journal.com Optical Imaging Approaches to Monitor Static and Dynamic Cell-on-Chip Platforms: A Tutorial Review Alireza Arandian, Zeinab Bagheri, Hamide Ehtesabi, Shima Najafi Nobar, Neda Aminoroaya, Ashkan Samimi, and Hamid Latifi* A. Arandian, N. Aminoraya, A. Samimi, Prof. H. Latifi Laser and Plasma Research Institute Shahid Beheshti University Tehran 1983969411, Iran E-mail: Latifi@sbu.ac.ir Dr. Z. Bagheri, Dr. H. Ehtesabi Faculty of Life Sciences and Biotechnology Shahid Beheshti University Tehran 1983969411, Iran Dr. S. Najafi Nobar Faculty of Mechanical Engineering K. N. Toosi University of Technology Tehran 1969764499, Iran Prof. H. Latifi Department of Physics Shahid Beheshti University Tehran 1983969411, Iran The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.201900737. DOI: 10.1002/smll.201900737 may be manipulated, treated or analyzed in a controllable and reproducible way. [1] Analyzing a significant number of bio- logical agents is crucial in many studies. Single cells on chips may be isolated in wells, traps or patterns [2] and could be monitored over time. Because of the fixed position of the aimed objects, these plat- forms are called static. On the other hand, in-motion cells on chips may be confined in moving structures such as flow constric- tions, fluid flow focusing, or microdrop- lets [2] which could be named as dynamic platforms. In this paper, we consider motion of cells on platforms. The terms “static” and “dynamic” platforms should not be misconceived with similar terms in other literatures, where a motionless cell culture under the exposure of stag- nant or continuously changing medium is monitored with a microsensor. [3] While they consider the medium movement, in this review these terms are dedicated to the cell movement status. Both static and dynamic cell-on-chip platforms provide different biological applications in biosensors, drug screening, stem cells, genetic analysis, single cell analysis, and some other applications. [4] Passing behind the limitation of the naked eyes, optical microscopy opened up a new vision to the small world. In 1665, the first illustrated book on microscopy named “Micro- graphica” was published. The author, Robert Hooke is known for coining the word “cell”. [5] Simple magnification was the key feature of the early microscopes. However, that was enough for the greatest breakthroughs in biology for prognosis, diagnosis and treatment. Still today, optical imaging is a significant part of a lot of studies. A sample to be observable must be a light diffuser or a light producer. In other words, imaging signals are generated as a result of light scattering or light emission from a sample. Light scattering occurs over a broad range of incident wavelengths. Scattering effect may be elastic or inelastic. In elastic scattering, the energy of the scattered photon is the same as the energy of the incident photon and therefore, there is no wavelength shift. Rayleigh- and Mie-scatterings are two kinds of elastic scattering effects at the presence of particles whose sizes are much smaller or comparable to the wavelength of incident light, respectively. [6] In inelastic scattering, light is scattered at the wavelengths greater or smaller than the wavelength of the Miniaturized laboratories on chip platforms play an important role in han- dling life sciences studies. The platforms may contain static or dynamic biological cells. Examples are a fixed medium of an organ-on-a-chip and indi- vidual cells moving in a microfluidic channel, respectively. Due to feasibility of control or investigation and ethical implications of live targets, both static and dynamic cell-on-chip platforms promise various applications in biology. To extract necessary information from the experiments, the demand for direct monitoring is rapidly increasing. Among different microscopy methods, optical imaging is a straightforward choice. Considering light interaction with biological agents, imaging signals may be generated as a result of scattering or emission effects from a sample. Thus, optical imaging techniques could be categorized into scattering-based and emission-based techniques. In this review, various optical imaging approaches used in monitoring static and dynamic platforms are introduced along with their optical systems, advan- tages, challenges, and applications. This review may help biologists to find a suitable imaging technique for different cell-on-chip studies and might also be useful for the people who are going to develop optical imaging systems in life sciences studies. Optical Bio-Imaging 1. Introduction Cells as building blocks of biological structures have always been interesting to be monitored. Cell chip is a relatively new tool that can be defined as a miniaturized device in which cells Small 2019, 1900737