The ongoing race of biomedical applications has given momentum to the development of graphene quantum dots (GQDs). GQDs are zero-dimensional fluorescent carbon-nanomaterials, with a pronounced quantum confinement effect, and abundant edge states and functional groups. Despite their potential applications, mass-scale synthesis of single crystalline graphene quantum dots (GQDs) with high quantum yields derived via a direct green synthesis approach from bio-wastes is a major challenge. Hitherto, green extract (i.e. sugarcane molasses) driven single crystalline sulphur-doped GQDs (S-GQDs) with a longer decay time, high quantum yield, and excellent biocompatibility have remained unexplored in the bioimaging arena. At the same time, this agro-industrial waste has value in terms of both products and byproducts i.e. zero waste generation resulting in reduced human footprint on the environment. For the first time, we present a facile, large-scale, one-step, economical, template- and catalyst-free synthesis of sustainable, highly crystalline S-GQDs via a hydrothermal route from second generation (2G) bio-wastes. Mechanistic insight into the formation of S-GQDs from their precursor was obtained using powder X-ray diffraction patterns (PXRD). S-GQDs directly obtained from bio-wastes without surface passivation showed the highest quantum yield (QY) ∼ 47% obtained to date. The wide and symmetric emission spectrum of these S-GQDs is instrumental for sensitive detection as labelling nanoprobes. Moreover, their non-toxic behavior, in vitro and in vivo, has a future in quick point-of-care screening and real-time bioimaging. Thus, the as-synthesized bio-waste derived S-GQDs accomplished the purpose of an advanced environmentally friendly and sustainable material which is non-toxic, viable, safe, and cheap. This unprecedented work advances the synthesis of high-quality S-GQDs from bio-waste, which provides a breakthrough in the bioimaging field.

A variety of pH responsive hydrogels possessing macroporous interiors resembling a honey-comb framework with a continuous skin on the surface have been developed by free radical aqueous copolymerization of acrylic acid (AAc) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) (poly(AAc-co-DMAEMA) (PAD) hydrogels). This one step polymerization process makes scaling-up easier for mass production. Our formulations, being devoid of any chemical cross-linkers, remained dimensionally stable in buffer solutions of pH 1.2–7.4 with interlocked nanogels being identified as the building blocks of the network structures. Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), uniaxial compression testing and scanning electron microscopy (SEM) were used to characterize the hydrogels (PADs). Compressive elastic modulus and compressive strength of the swollen hydrogels at pH 7 were found to vary with composition from ∼3 to ∼11 kPa and ∼178 to ∼206 kPa, respectively. The swollen gels showed fairly strong viscoelastic behaviour and underwent deformation from ∼70% to 85% before failure, indicating the formation of robust 3D structures of PADs. Preliminary investigation into the biocompatibility of our hydrogels done by cytotoxicity assays using HeLa and McCoy mouse fibroblast cell lines have revealed that they are non-cytotoxic, paving the way for further biomedical applications. Swelling behaviour and release kinetics of bovine serum albumin (BSA) were investigated in various buffer solutions that mimic the pH-metric hierarchy in the gastrointestinal (GI) tract. Equilibrium swelling ratio was found to vary from 171% (mass) to 2027% (mass) depending on the pH and composition of hydrogels. Different compositions of PAD systems were investigated to verify the possibility of tailor-making the drug release behaviour of PAD formations.

Nanotechnology advancements and applications have paved the way for new possibilities in regenerative medicine and tissue engineering. It is a relatively new field that has the potential to improve stem cell differentiation and therapy greatly. Numerous studies have demonstrated that nanomaterials can function as a physiological niche for the formation and differentiation of stem cells. However, quantum dots (QDs), such as carbon quantum dots (CQDs) and graphene quantum dots (GQDs), have shown considerable promise in the field of regenerative medicine. To date, most research has focused on stem cell tracking and imaging using CQDs. However, their interaction with stem cells and the associated possibility for differentiation by selectively focusing chemical signals to a particular lineage has received scant attention. In this mini-review, we attempt to categorize a few pathways linked with the role of CQDs in stem cell differentiation.