As opposed to inorganic counterparts, organic quantum dots often exhibit lower fluorescence efficiencies and are complex to synthesize. Here we develop nitrogen‐doped (N‐GQDs) and nitrogen–sulfur codoped (NS‐GQDs) graphene quantum dots exhibiting high‐yield visible and near‐IR emission that are synthesized via a single‐step microwave‐assisted hydrothermal technique with a single glucosamine‐HCl starting material (thiourea precursor used for NS‐GQDs). As‐synthesized N‐GQDs and NS‐GQDs are well‐dispersed (average sizes of 5.50 and 3.90 nm) with high crystallinity and pronounced G‐band. Formed by the bottom‐up assembly of glucosamine, they contain amine linkage and a variety of oxygen‐containing functional groups assessed by Fourier‐transform infrared spectroscopy with ≈2% sulfur for NS‐GQDs. The synthetic procedure allows varying their size and the bandgap. Unlike other graphene‐based quantum dots, these GQDs exhibit bright, stable fluorescence both in the visible and near‐IR with high quantum yields of up to 60%. Excitation‐dependent visible fluorescence is attributed to size‐dependent bandgaps, with near‐IR emission potentially arising from the emissive defect states/their arrangements. Advantageous properties of these GQDs are utilized to develop exciton recombination layer for organic light‐emitting devices exhibiting both photoluminescence and electroluminescence in the visible. Produced by ecofriendly one‐step scalable synthesis brightly‐emissive N‐GQDs and NS‐GQDs become a promising material for novel organic optoelectronics.

Despite significant advances of nanomedicine, the issues of biocompatibility, accumulation-derived toxicity, and the lack of sensing and in vivo imaging capabilities hamper the translation of most nanocarriers into clinic. To address this, we utilize nitrogen, boron/ nitrogen, and sulfur-doped graphene quantum dots (GQDs) as fully biocompatible multifunctional platforms allowing for multicolor visible/ near-IR imaging and cancer-sensing. These GQDs are scalably produced in one-step synthesis from a single biocompatible glucosamine precursor, are water-soluble, show no cytotoxicity at high concentrations of 1 mg/mL, and demonstrate substantial degradation at 36 h in biological environments as verified by TEM imaging. Because of their small sizes, GQDs exhibit efficient internalization maximized at 12 h followed by further degradation/excretion. Their high-yield intrinsic fluorescence in blue/ green and near-infrared allows for multicolor in vitro imaging on its own or in combination with other fluorophores, and offers the capabilities for in vivo near-IR fluorescence tracking. Additionally, nitrogen-and sulfur-doped GQDs exhibit pH-dependent fluorescence response that is successfully utilized as a sensing mechanism for acidic extracellular environments of cancer cells. It allows for the deterministic, ratiometric spectral discrimination between cancerous (HeLa and MCF-7 cell) versus healthy (HEK-293 cell) environments with substantial intensity ratios of 1.6 to 8. These results suggest fully biocompatible GQDs developed in this work as multifunctional candidates for in vitro delivery of active agents, multicolor visible/near-IR fluorescence imaging, and pH-sensing of cancerous environments.

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A general method for the formation of a broad family of silicon nanotube arrays (Si NTAs) relevant to diverse fields--ranging from energy storage to therapeutic platforms--is described. Such nanotubes demonstrate a thickness-dependent dissolution behavior important to its potential use in drug delivery. Under selected conditions, novel porous silicon nanotubes can be prepared when the shell thickness is on the order of 12 nm or less, capable of being loaded with small molecules such as luminescent ruthenium dyes associated with dye-sensitized photovoltaic devices.

Graphene oxide (GO) is a graphene derivative that emits fluorescence, which makes GO an attractive material for optoelectronics and biotechnology. In this work, we utilize ozone treatment to controllably tune the band gap of GO, which can significantly enhance its applications. Ozone treatment in aqueous GO suspensions yields the addition/rearrangement of oxygen-containing functional groups suggested by the increase in vibrational transitions of C-O and C=O moieties. Concomitantly it leads to an initial increase in GO fluorescence intensity and significant (100 nm) blue shifts in emission maxima. Based on the model of GO fluorescence originating from sp2 graphitic islands confined by oxygenated addends, we propose that ozone-induced functionalization decreases the size of graphitic islands affecting the GO band gap and emission energies. TEM analyses of GO flakes confirm the size decrease of ordered sp2 domains with ozone treatment, whereas semi-empirical PM3 calculations on model addend-confined graphitic clusters predict the inverse dependence of the band gap energies on sp2 cluster size. This model explains ozone-induced increase in emission energies yielding fluorescence blue shifts and helps develop an understanding of the origins of GO fluorescence emission. Furthermore, ozone treatment provides a versatile approach to controllably alter GO band gap for optoelectronics and bio-sensing applications.