Highly water-soluble, biocompatible, and photoluminescent carbon nanodots (C-dots) having an average diameter 3.4 AE 0.8 nm and a quantum yield 4.3% are obtained from used green tea through grinding, calcination and centrifugation. The as-prepared C-dots are stable in high-ionic-strength media (e.g. 500 mM NaCl) and under light irradiation, allowing images of MCF-10A, MCF-7 and MDA-MB-231 cells to be recorded. The C-dots are mostly localized in the cell membranes and cytoplasms, with evidence of excitation-wavelength cell images. Relative to catechin, the C-dots provide greater inhibition efficiency of the growth of MCF-7 and MDA-MB-231 cancer cells, with lower toxicity for the MCF-10A normal cells. The inhibitory activity of C-dots is associated with the generation of greater amounts of reactive oxygen species. A prothrombin time (PT) assay of plasma samples reveals excellent biocompatibility of the C-dots. To the best of our knowledge, for the first time the C-dots provide inhibition efficiencies up to 80% and 82% for MCF-7 and MDA-MB-231 cancer cells, respectively, showing their high potential as cancer inhibitors.

We report the synthesis of fluorescent 11-mercaptoundecanoic acid-gold nanodot-liposome (11-MUA-Au ND/Lip) hybrids by incorporation of gold nanoparticles (∼3 nm) and 11-MUA molecules in hydrophobic phospholipid membranes that self-assemble to form small unilamellar vesicles. A simple and homogeneous fluorescence assay for phospholipase C (PLC) was developed on the basis of the fluorescence quenching of 11-MUA-Au ND/Lip hybrids in aqueous solution. The fluorescence of the 11-MUA-Au ND/Lip hybrids is quenched by oxygen (O2) molecules in solution, and quenching is reduced in the presence of PLC. PLC catalyzes the hydrolysis of phosphatidylcholine units from Lip to yield diacylglycerol (DAG) and phosphocholine (PC) products, leading to the decomposition of Lip. The diacylglycerol further interacts with 11-MUA-Au NDs via hydrophobic interactions, leading to inhibition of O2 quenching. The 11-MUA-Au ND/Lip probe provides a limit of detection (at a signal-to-noise ratio of 3) of 0.21 nM for PLC, with high selectivity over other proteins, enzymes, and phospholipases. We have validated the practicality of using this probe for the determination of PLC concentrations in breast cancer cells (MCF-7 and MDA-MB-231 cell lines) and nontumor cells (MCF-10A cell line), revealing that the PLC activity in the first two is at least 1.5-fold higher than that in the third. An inhibitor assay using 11-MUA-Au ND/Lip hybrids demonstrated that tricyclodecan-9-yl potassium xanthate (D609) inhibits PLC (10 nM) with an IC50 value of 3.81 ± 0.22 μM. This simple, sensitive, and selective approach holds great potential for detection of PLC in cancer cells and for the screening of anti-PLC drugs.

Poly(N-isopropylacrylamide) microgels (PNIPAM MGs) incorporated with photoluminescent gold nanodots (Au NDs) have been prepared and employed for the detection of mercury ions (Hg(2+)). Each of the PNIPAM MGs (hydrodynamic diameter 615 ± 15 nm) contains several Au NDs (diameter 1.8 ± 0.2 nm) in the Au ND-PNIPAM MGs. Like Au NDs, Au ND-PNIPAM MGs exhibit an absorption band at 375 nm that is assigned for ligand to metal charge transfer mixed with metal centered (ds/dp) states and photoluminescence at 520 nm originated from Au ND/polynuclear gold(I)-thiolate (core/shell) complexes. Purification of Au ND-PNIPAM MGs relative to Au NDs is much easier through a simple centrifugation/wash process. On the basis of Hg(2+)-induced photoluminescence quenching due to the formation of Au-Hg amalgam and formation of Au ND-PNIPAM MGs aggregates, the signal response of Au ND-PNIPAM MGs against Hg(2+) concentration is linear over a range from 2 to 20 nM (r = 0.9945). This selective approach provides limits of detection for Hg(2+) (at a signal-to-noise ratio of 3) of 1.9 and 1.7 nM in phosphate buffer solutions (5 mM, pH 7.0) with and without containing 500 mM NaCl, respectively. This selective and sensitive Au ND-PNIPAM MG probe has been applied to the determination of the concentration of Hg in a representative fish sample, showing its practical potential for monitoring of Hg levels in complicated biological and environmental samples.

We have developed aptamer (Apt)-conjugated gold nanoparticles (Apt-Au NPs, 13 nm in diameter) as highly effective inhibitors for human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT). Two Apts, RT1t49 (Aptpol) and ODN 93 (AptRH), which recognize the polymerase and RNase H regions of HIV-1 RT, are used to conjugate Au NPs to prepare Aptpol-Au NPs and AptRH-Au NPs, respectively. In addition to DNA sequence, the surface density of the aptamers on Au NPs (nApt-Au NPs; n is the number of aptamer molecules on each Au NP) and the linker length number (Tm; m is the base number of the deoxythymidine linker) between the aptamer and Au NPs play important roles in determining their inhibition activity. A HIV-lentiviral vector-based antiviral assay has been applied to determine the inhibitory effect of aptamers or Apt-Au NPs on the early stages of their replication cycle. The nuclease-stable G-quadruplex structure of 40AptRH-T45-Au NPs shows inhibitory efficiency in the retroviral replication cycle with a decreasing infectivity (40.2%).

A facile, one-pot synthetic approach has been developed for the preparation of BSA-Ce/Au NCs. The fluorescence intensities of BSA-Ce/Au NCs at 410 and 650 nm are pH dependent and independent, respectively. The fluorescence intensity ratio (I410/I650) is linear against pH values from 6.0 to 9.0. These stable and biocompatible BSA-Ce/Au NCs have been used as ratiometric probes for monitoring local pH values inside HeLa cells.