This article reports the development of an optical imaging technique, confocal light absorption and scattering spectroscopic (CLASS) microscopy, capable of noninvasively determining the dimensions and other physical properties of single subcellular organelles. CLASS microscopy combines the principles of light-scattering spectroscopy (LSS) with confocal microscopy. LSS is an optical technique that relates the spectroscopic properties of light elastically scattered by small particles to their size, refractive index, and shape. The multispectral nature of LSS enables it to measure internal cell structures much smaller than the diffraction limit without damaging the cell or requiring exogenous markers, which could affect cell function. Scanning the confocal volume across the sample creates an image. CLASS microscopy approaches the accuracy of electron microscopy but is nondestructive and does not require the contrast agents common to optical microscopy. It provides unique capabilities to study functions of viable cells, which are beyond the capabilities of other techniques.

We have developed a novel optical method for observing submicrometer intracellular structures in living cells, which is called confocal light absorption and scattering spectroscopic (CLASS) microscopy. It combines confocal microscopy, a well-established high-resolution microscopic technique, with light-scattering spectroscopy. CLASS microscopy requires no exogenous labels and is capable of imaging and continuously monitoring individual viable cells, enabling the observation of cell and organelle functioning at scales of the order of 100 nm.

This article reviews the application of optical diagnostic technology based on light scattering spectroscopy for minimally invasive detection of precancerous and early cancerous changes in a variety of organs. Optical spectroscopic techniques have shown promising results in the diagnosis of diseases at the cellular scale. They do not require tissue removal, can be performed in vivo and allow for real-time diagnosis. While fluorescence and Raman spectroscopy are most effective in revealing the molecular properties of tissue, the novel technique, light scattering spectroscopy, is capable of characterizing the structural properties of tissue at the cellular and subcellular scale.

This paper reports the evolution of scanning spectral imaging techniques using scattered light for minimally invasive detection of early cancerous changes in tissue and cell biology applications. Optical spectroscopic techniques have shown promising results in the diagnosis of disease on a cellular scale. They do not require tissue removal, can be performed in vivo, and allow for real-time diagnoses. Fluorescence and Raman spectroscopy are most effective in revealing molecular properties of tissue. Light scattering spectroscopy (LSS) relates the spectroscopic properties of light elastically scattered by small particles, such as epithelial cell nuclei and organelles, to their size, shape, and refractive index. It is capable of characterizing the structural properties of tissue on cellular and subcellular scales. However, in order to be useful in the detection of early cancerous changes that are otherwise not visible to the naked eye, it must rapidly survey a comparatively large area while simultaneously detecting these cellular changes. Both goals are achieved by combining LSS with spatial scanning imaging. Two examples are described in this paper. The first reviews a clinical system for screening patients with Barrett's esophagus. The second presents a novel advancement in confocal light absorption and scattering spectroscopic microscopy.

The biggest challenge in using CRISPR technologies, which limits their widespread application in medicine, is off-target effects. These effects could, in principle, be minimized by ensuring that CRISPR is activated primarily in the targeted cells, thereby reducing the likelihood of unintended genetic modifications in non-target tissues. Therefore, the development of a light activatable CRISPR approach to dynamically control gene activation in both space and time would be highly beneficial. A drawback is that the overwhelming majority of recently introduced light activatable CRISPR systems require UV or blue light exposure, severely limiting the penetration depth of light in tissue at which CRISPR can be activated, and, in the case of UV light, raising safety concerns. A small number of systems that activate CRISPR using longer wavelengths are hindered by either slow light activation or issues related to toxicity and biocompatibility of the proposed techniques in humans. To address this, we developed a split-Cas9/dCas9 system in which activation is achieved through a near-infrared photocleavable dimerization complex. This photoactivation method can be safely used in humans in vivo, easily adapted to different split-Cas9/dCas9 systems, and enables rapid, spatially precise light activation across various cell types.

Gold nanorods can be used as extremely bright labels for differential light scattering measurements using two closely spaced wavelengths, thereby detecting human disease through several centimeters of tissue in vivo. They have excellent biocompatibility, are non-toxic, and are not susceptible to photobleaching. They have narrow, easily tunable plasmon spectral lines and thus can image multiple molecular targets simultaneously. Because of their small size, gold nanorods can be transported to various tissues inside the human body via the vasculature and microvasculature, and since they are smaller than vascular pore sizes, they can easily cross vascular space and enter individual cells.