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Fluorescent nanodiamonds (FNDs) have been attracting much attention as promising therapeutic agents and probes for bioimaging and nanosensing. For their biological applications, several hydrophilizing methods to enhance FND colloidal stability have been developed to suppress their aggregation and the nonspecific adsorption to biomolecules in complex biomedical environments. However, these methods involve several complicated synthetic and purification steps, which prohibit the use of FNDs for bioapplications by biologists. In this study, we describe a simple one-pot FND hydrophilization method that comprises coating of the surface of the nanoparticles with COOH-terminated hyperbranched polyglycerol (HPG-COOH). HPG-COOH-coated FNDs (FND-HPG-COOHs) were found to exhibit excellent dispersibility under physiological conditions despite the thinness of the 5 nm HPG-COOH layer. Biotinylated FND-HPG-COOHs specifically captured avidin molecules in the absence of nonspecific protein adsorption. Moreover, we demonstrated that FND-HPG-COOHs conjugated with antibodies can be used to selectively target integrins in fixed HeLa cells. In addition, intracellular temperature changes were measured via optically detected magnetic resonance using FND-HPG-COOHs conjugated with mitochondrial localization signal peptides. Our one-pot synthetic method will encourage the broad use of FNDs among molecular and cellular biologists and pave the way for extensive biological and biomedical applications of FNDs.

Nanodiamonds containing negatively charged nitrogen-vacancy (NV-) centers are versatile nanosensors thanks to their optical and spin properties. While currently most fluorescent nanodiamonds in use have at least a size of a few tens of nanometers, the challenge lies in engineering the smallest nanodiamonds containing a single NV- defect. Such a tiny nanocrystal with a single NV- center is an "optical spin label" for biomolecules, which can be detected in a fluorescence microscope. In this paper, we address two key issues toward this goal using detonation nanodiamonds (DNDs) of 4-5 nm in size. The DND samples are treated first with electron irradiation to create more vacancies. With the aid of electron paramagnetic resonance (EPR) spectroscopy, we confirm a steady increase of negatively charged NV- centers with higher fluence. This leads to a 4 times higher concentration in NV- defects after irradiation with 2 MeV electrons at a fluence of 5 × 1018 e-/cm2. Interestingly, we observe that the annealing of DND does not increase the number of NV- centers, which is in contrast to bulk diamond and larger nanodiamonds. Since DNDs are strongly aggregated after the irradiation process, we apply a boiling acid treatment as a second step to fabricate monodisperse DNDs enriched in NV- centers. These are two important steps toward "optical spin labels" having a single-digit nanometer range size that could be used for bioimaging and nanosensing.

Introducing nanomaterial in interfacial polymerization (IP) system for nanofiltration (NF) membrane synthesis has witnessed a remarkable performance enhancement thus drawing intensive attention. However, the underlying mechanism for nanomaterial induced performance enhancement is still unclear due to the lack of study on nanoparticle dispersity and architecture at polymerization interface. Using nanodiamond (ND) as the example, this study demonstrates nanoparticle undergoes aggregation preferably at the reaction interface and the architecture of ND particles has a direct impact on membrane structure and performance. Through proactively controlling the aggregation extent while employing these ND clusters as the nano-template, the feature morphology of NF membrane is transformed from nodules to ridges at the nanoscale. Such transformation generates a significant augmentation of effective membrane area, leading to the increase of water permeance by 70%. With a low amount of nanodiamond addition (

Background Nanodiamonds (NDs) provide a unique multitasking system for drug delivery and fluorescent imaging in biological environments. Owing to their quantum properties, NDs are expected to be employed as multifunctional probes in the future for the accurate visualization of biophysical parameters such as temperature and magnetic fields. However, the use of NDs for the selective targeting of the biomolecules of interest within a complicated biological system remains a challenge. One of the most promising solutions is the appropriate surface design of NDs based on organic chemistry and biochemistry. The engineered NDs have high biocompatibility and dispersibility in a biological environment and hence undergo cellular uptake through specific pathways. Scope of review This review focuses on the selective targeting of NDs for biomedical and biophysical applications from the viewpoint of ND surface functionalizations and modifications. These pretreatments make possible the specific targeting of biomolecules of interest on or in a cell by NDs via a designed biochemical route. Major conclusions The surface of NDs is covalently or noncovalently modified with silica, polymers, or biomolecules to reshape them, control their size, and enhance the colloidal stability and biomolecular selectivity toward the biomolecules of interest. Electroporation, chemical treatment, injection, or endocytosis are the methods generally adopted to introduce NDs into living cells. The pathway, efficiency, and the cell viability depend on the selected method. General significance In the biomedical field, the surface modification facilitates specific delivery of a drug, leading to a higher therapeutic efficacy. In biophysical applications, the surface modification paves the way for the accurate measurement of physical parameters to gain a better understanding of various cell functions.