Fluorescence probes are essential for in vivo molecular imaging as well as cell tracking applications. Probes that emit in the far red wavelength penetrate better through biological tissue and the autofluorescence background is reduced at higher wavelengths, making such probes highly desirable. We report the application of Graphene Quantum Dots (GQDs) as efficient fluorescence probes for single cell tracking using high-resolution confocal microscopy as well as a potential in vivo fluorescent imaging agent. High-quality water soluble GQDs were synthesized by ablating highly oriented pyrolytic graphite (HOPG) in liquid using a nanosecond pulsed laser. Refluxing GQDs at 200 °C for 20 minutes and 1 hour produces excitation independent broad emission peaking at 600 nm and excitation dependent color-tunable emission, respectively. These emission properties can be attributed to the functional groups such as carboxyl and hydroxyl groups on the surface or edges. MTT assays with the breast cancer (MCF-7) cell line suggest that 20 min and 1 h GQDs had 80% viability post incubation with concentrations as high as 2 mg mL⁻¹. The paper also explores the molecular tracking functionality of GQDs. Fluorescence microscopy showed that MCF-7 cells incubated for up to 48 hours with GQDs, internalized the GQDs, by caveolae-mediated endocytosis without any targeting moiety. In addition, high-resolution Z stacking and 3D confocal microscopy of a single live MCF-7 cell confirm successful uptake of GQDs into the cytoplasm by endocytosis. Fluorescence imaging of GQDs loaded in polyacrylamide gel and subcutaneously implanted near the thoracic region of an euthanized mice was done to explore the feasibility of in vivo imaging using GQDs. Deep red fluorescence (610 nm emission filter) was observed from the implanted region with relatively low autofluorescence background.

CD44 receptor mediated the uptake of DOX-HA-Cys-CNG by colon cancer cells and the redox responsive release of DOX by the intracellular GSH.

Recently, considerable interest has emerged in the development of biosensors to detect biomarkers and immune checkpoints to identify and measure cancer through liquid biopsies. The detection of cancer biomarkers from a small volume of blood is relatively fast compared to the gold standard of tissue biopsies. Traditional immuno-histochemistry (IHC) requires tissue samples obtained using invasive procedures and specific expertise as well as sophisticated instruments. Furthermore, the turnaround for IHC assays is usually several days. To overcome these challenges, on-demand biosensor-based assays were developed to provide more immediate prognostic information for clinicians. Novel rapid, highly precise, and sensitive approaches have been under investigation using physical and biochemical methods to sense biomarkers. Additionally, interest in understanding immune checkpoints has facilitated the rapid detection of cancer prognosis from liquid biopsies. Typically, these devices combine various classes of detectors with digital outputs for the measurement of soluble cancer or immune checkpoint (IC) markers from liquid biopsy samples. These sensor devices have two key advantages: (a) a small volume of blood drawn from the patient is sufficient for analysis, and (b) it could aid physicians in quickly selecting and deciding the appropriate therapy regime for the patients (e.g., immune checkpoint blockade (ICB) therapy). In this review, we will provide updates on potential cancer markers, various biosensors in cancer diagnosis, and the corresponding limits of detection, while focusing on biosensor development for IC marker detection.