Sensitive detection of nonfluorescent solutes in small amounts of dilute aqueous solutions through photothermally induced reflectivity modulation at glass/aqueous solution interfaces

In this study, we propose employing photothermal reflectance (PTR) spectroscopy, typically used to assess the thermal properties of solid materials, for detecting nonluminescent solutes in small amounts of dilute aqueous solutions. In this spectroscopy, a probe beam nonresonant and a pump beam resonant to the solution are focused on a transparent material/aqueous solution interface. As the temperature coefficients of refractive indexes depend on the media, the heat from the pump beam absorption changes the reflectivity at the material/solution interface. A limit of detection of 75 nM was achieved for an interface at a glass and an aqueous solution of a dye. Among various photothermal spectroscopic techniques, a notable advantage of reflectance spectroscopy is its straightforward optical configuration, where neither a precisely aligned beam expander nor a differential beam splitting is required, making the optical system inexpensive and reproducible. Since reflectance spectroscopy only requires a material/solution interface, it is applicable to solutions confined to micrometer-sized channels or pits, enabling the analysis of samples with trace amounts.

Integrated heart/cancer on a chip to reproduce the side effects of anti-cancer drugs in vitro

Integrated Heart/Cancer on a Chip (iHCC) is a promising microfluidic platform that allows the culture of different cell types separately and application of closed-medium circulation to reproduce the side effects of doxorubicin on heart in vitro.

Imaging live cells at high spatiotemporal resolution for lab-on-a-chip applications

Conventional optical imaging techniques are limited by the diffraction limit and difficult-to-image biomolecular and sub-cellular processes in living specimens. Novel optical imaging techniques are constantly evolving with the desire to innovate an imaging tool that is capable of seeing sub-cellular processes in a biological system, especially in three dimensions (3D) over time, i.e. 4D imaging. For fluorescence imaging on live cells, the trade-offs among imaging depth, spatial resolution, temporal resolution and photo-damage are constrained based on the limited photons of the emitters. The fundamental solution to solve this dilemma is to enlarge the photon bank such as the development of photostable and bright fluorophores, leading to the innovation in optical imaging techniques such as super-resolution microscopy and light sheet microscopy. With the synergy of microfluidic technology that is capable of manipulating biological cells and controlling their microenvironments to mimic in vivo physiological environments, studies of sub-cellular processes in various biological systems can be simplified and investigated systematically. In this review, we provide an overview of current state-of-the-art super-resolution and 3D live cell imaging techniques and their lab-on-a-chip applications, and finally discuss future research trends in new and breakthrough research areas of live specimen 4D imaging in controlled 3D microenvironments.