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Carbon dots have been gaining attention in the field of nanobiotechnology due to their superior photostability, high water solubility, ease of synthesis and surface functionalization, chemical inertness, low toxicity, and excellent biocompatibility. They also exhibit good two-photon absorption and unique tunable optical properties across a wide range of wavelengths, from ultraviolet to near infrared endowing them with potential for a variety of biological applications. Recently, there has been a growing interest in the synthesis and development of red-emissive two-photon carbon dots. Here we present recent progress in the design requirements for red-emissive two-photon carbon dots, and review current state-of-the-art systems, covering their applications in bioimaging, biosensing, and photothermal and photodynamic therapy. Carbon dots are suitable for a range of biological applications due to their unique physicochemical properties and biological behavior. This Review summarizes research related to the emerging field of red-emissive two-photon carbon dots for bioimaging, biosensing, and phototherapeutic applications.

Designing a two-photon ratiometric pH-sensitive nanoprobe for real time monitoring of intracellular pH in biological environment is of great importance for better understanding the pathogenesis of diseases and the design of intracellular drug delivery-based system. However, the development of such probe remains a challenge. Here, we report for the first time the design and development of the two-photon ratiometric carbon dot-based nanoprobe and demonstrate its capability to monitor and quantify the intracellular cytoplasmic pH value, in real time. The nanoprobe comprised of a fluorescent carbon dot functionalized with a pH-responsive fluorescein dye (FACD). With increasing pH, FACD exhibits a clear ratiometric change in the emission intensity ratio, with sensitivity across a wide pH range in both extracellular and intracellular compartments. FACD is non-toxic to adipose stem cells in cell imaging experimental conditions and exhibits remarkable thermal stability, photostability, and two-photon near-infrared excitation capability. Using real-time dual-channel two-photon confocal microscopy we demonstrate the great potential of FACD as an efficient nanoprobe with high accuracy for the intracellular sensing of pH in living adipose stem cells seeded on either cell-culture dishes or on a 3D printed bioactive scaffold.

Nanoparticles are key vehicles for targeted therapies because they can pass through biological barriers, enter into cells, and distribute within cell structures. We investigated the synthesis of blue and green emissive hexagonal boron nitride quantum dots (hBNQDs) using a liquid-exfoliation technique followed by hydrothermal treatment. A distinct shift from blue to bright-green emission was observed upon surface passivating the dots using poly(ethylene glycol) or PEG200 under the same UV irradiation. The quantum yield of the hBNQDs increased with the surface passivation. Multiplexed imaging was accomplished using the hBNQDs in conjunction with organic dyes. The hBNQDs provided images with distinctive emission wavelengths and fluorescence lifetimes. Although the fluorescence signals of blue- and green-emissive hBNQDs overlap spectrally with those of the emission wavelengths of the organic dyes, the fluorescence lifetime data were resolved temporally using software-based time gates. The blue-emissive hBNQD-...

Carbon based quantum dots find various applications such as imaging, diagnosis and therapeutics due to low toxicity, antibacterial activity, excellent water solubility, and good biocompatibility. However, the UV-blue emission of carbon based quantum dots is unsuited for applications in biomedicine and imaging as the short wavelength lights harm the living cells due to phototoxicity. In the present work, we have synthesised the long wavelength emitting heteroatoms (nitrogen (N) and sulfur (S)) co-doped graphene quantum dots (NS-GQD) via hydrothermal route. These NS-GQD have excitation-wavelength independent photoluminescence with high quantum yield in protonated and neutral forms. The non-covalent interaction of these NS-GQD when studied with a dye rhodamine B (RB) shows evidence of Forster resonance energy transfer (FRET). It has been shown here that the NS-GQD-RB composite exhibits prominent two-photon absorption at near infrared wavelength with a capability of deep-tissue imaging upto 175 µm.

Nanostructured manganese cobaltite spinel oxide (MnCo 2 O 4 ) was successfully synthesized by co-precipitation method. X-ray diffraction (XRD) results revealed that the molar ratio of OH − / NO 3 − = 1.5 in the precipitation stage is more appropriate for achieving MnCo 2 O 4 phase. The results of thermal analysis (TGA/DTA) along with the XRD results revealed that the MnCo 2 O 4 phase remains stable up to 1050 °C. Morphological studies show that by increasing the calcination temperature from 350 to 550 and 1000 °C, morphology of the particles varies from plate-like to quasi spherical and polyhedral shape, respectively. Density and porosity measurement of cold pressed and sintered samples showed that by employing un-calcined powder, a dense sample with 98% of the theoretical density could be obtained at the sintering temperature of 1000 °C. Selected synthesized powders were coated on the AISI 430 ferritic stainless steel coupons and the results demonstrated that using un-calcined powder, leads to the formation of a highly dense and adhesive coating layer due to the very high tendency of un-calcined powder for densification.