Scott G. Harroun

Immobilization of aptamer-modified gold nanoparticles on BiOCl nanosheets: Tunable peroxidase-like activity by protein recognition.

A self-assembled nanocomposite is prepared from an aqueous mixture of aptamer-modified gold nanoparticles (Apt-Au NPs), bismuth ions and chloride ions. The Apt-Au NPs are immobilized on bismuth oxychloride (BiOCl) nanosheets in situ to form Apt-Au NPs/BiOCl nanocomposites. The as-prepared nanocomposites exhibit high peroxidase-like activity for the catalytic conversion of Amplex Red (AR) to fluorescent resorufin in the presence of H2O2. The catalytic activity of Apt-Au NPs/BiOCl nanocomposites is at least 90-fold higher than that of Apt-Au NPs or BiOCl nanosheets, revealing synergistic effects on their activity. The catalytic activity of Apt-Au NPs/BiOCl nanocomposites is suppressed by vascular endothelial growth factor-A165 (VEGF-A165) molecules that specifically interact with the aptamer units (Del-5-1 and v7t-1) on the nanocomposite surface. The AR/H2O2-Apt-Au NPs/BiOCl nanocomposites probe shows high selectivity (>1000-fold over other proteins) and sensitivity (detection limit ~0.5nM) for the detection of VEGF-A165. Furthermore, the probe is employed for the detection of VEGF isoforms and for the study of interactions between VEGF and VEGF receptors. The practicality of this simple, rapid, cost-effective probe is validated by the analysis of VEGF-A165 in cell culture media, showing its great potential for the analysis of VEGF in biological samples.

Super-Cationic Carbon Quantum Dots Synthesized from Spermidine as an Eye Drop Formulation for Topical Treatment of Bacterial Keratitis

We have developed a one-step method to synthesize carbon quantum dots (CQDPAs) from biogenic polyamines (PAs) as an antibacterial agent for topical treatment of bacterial keratitis (BK). CQDs synthesized by direct pyrolysis of spermidine (Spd) powder through a simple dry heating treatment exhibit a solubility and yield much higher than those from putrescine and spermine. We demonstrate that CQDs obtained from Spds (CQDSpds) possess effective antibacterial activities against non-multidrug-resistant Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Salmonella enterica serovar Enteritidis bacteria and also against the multidrug-resistant bacteria, methicillin-resistant S. aureus. The minimal inhibitory concentration (MIC) of CQDSpds is ∼2500-fold lower than that of spermidine alone, demonstrating their strong antibacterial capabilities. Investigation of the possible mechanisms behind the antibacterial activities of the as-synthesized CQDSpds indicates that the super-cationic CQDSpds with small size (diameter ca. 6 nm) and highly positive charge (ζ-potential ca. +45 mV) cause severe disruption of the bacterial membrane. In vitro cytotoxicity, hemolysis, hemagglutination, genotoxicity, and oxidative stress and in vivo morphologic and physiologic cornea change evaluations show the good biocompatibility of CQDSpds. Furthermore, topical ocular administration of CQDSpds can induce the opening of the tight junction of corneal epithelial cells, thereby leading to great antibacterial treatment of S. aureus-induced BK in rabbits. Our results suggest that CQDSpds are a promising antibacterial candidate for clinical applications in treating eye-related bacterial infections and even persistent bacteria-induced infections.

Synthesis of Self‐Assembled Spermidine‐Carbon Quantum Dots Effective against Multidrug‐Resistant Bacteria

This study reports a two-step method to synthesize spermidine-capped fluorescent carbon quantum dots (Spd-CQDs) and their potential application as an antibacterial agent. Fluorescent carbon quantum dots (CQDs) are synthesized by pyrolysis of ammonium citrate in the solid state and then modified with spermidine by a simple heating treatment without a coupling agent. Spermidine, a naturally occurring polyamine, binds with DNA, lipids, and proteins involved in many important processes within organisms such as DNA stability, and cell growth, proliferation, and death. The antimicrobial activity of the as-synthesized Spd-CQDs (size ≈4.6 nm) has been tested against non-multidrug-resistant E. coli, S. aureus, B. subtilis, and P. aeruginosa bacteria and also multidrug-resistant bacteria, methicillin-resistant S. aureus (MRSA). The minimal inhibitory concentration value of Spd-CQDs is much lower (>25 000-fold) than that of spermidine, indicating their promising antibacterial characteristics. The mechanism of antibacterial activity is investigated, and the results indicate that Spd-CQDs cause significant damage to the bacterial membrane. In vitro cytotoxicity and hemolysis analyses reveal the high biocompatibility of Spd-CQDs. To demonstrate its practical application, in vitro MRSA-infected wound healing studies in rats have been conducted, which show faster healing, better epithelialization, and formation of collagen fibers when Spd-CQDs are used as a dressing material.

Biomarkers of cigarette smoking and DNA methylating agents: Raman, SERS and DFT study of 3-methyladenine and 7-methyladenine

3-Methyladenine and 7-methyladenine are biomarkers of DNA damage from exposure to methylating agents. For example, the concentration of 3-methyladenine increases significantly in the urine of cigarette smokers. Surface-enhanced Raman spectroscopy (SERS) has shown much potential for detection of biomolecules, including DNA. Much work has been dedicated to the canonical nucleobases, with comparatively fewer investigations of modified DNA and modified DNA nucleobases. Herein, Raman spectroscopy and SERS are used to examine the adsorption orientations of 3-methyladenine and 7-methyladenine on Ag nanoparticles. Density functional theory (DFT) calculations at the B3LYP level are used to support the conclusions via simulated spectra of the nucleobases and of Ag+/nucleobase complexes. The results herein show that 7-methyladenine adsorbs upright via its N3 and N9 atoms side, similarly to adenine. 3-Methyladenine adsorbs in a very tilted or flat orientation on the Ag nanoparticles. These findings will be useful for future SERS or other nanoparticle-based bioanalytical assays for detection of these methyladenines or other modified nucleobases.

Visual detection of cyanide ions by membrane-based nanozyme assay

In this paper, we report a simple one-step synthesis of well-dispersed amorphous cobalt hydroxide/oxide-modified graphene oxide (CoOxH-GO) possessing peroxidase-like catalytic activity, and its application for the detection of H2O2, glucose, and CN- ions. CoOxH is formed and deposited in situ on the GO surface through the reaction between GO (size ~ 240nm) and Co2+ in basic solution at room temperature. We investigated the enzyme-mimicking activity of the CoOxH-GO nanohybrid in detail via the H2O2-mediated oxidation of Amplex Red (AR) to form fluorescent resorufin. The peroxidase-like activity of CoOxH-GO is utilized herein for the quantitation of H2O2 in a wide concentration range, from 100nM to 100μM. When coupled with glucose oxidase (GOD), the AR/CoOxH-GO system can determine glucose level in blood samples. Interestingly, cyanide ions (CN-) significantly inhibit the catalytic activity of the CoOxH-GO nanohybrid, which allows for the construction of a probe for the detection of CN- in water samples and laboratory wastes. We fabricated a membrane-based CoOxH-GO probe for the visual detection of CN- by preparing a thin film of CoOxH-GO on a positively charged and porous nylon membrane (N+M). The CoOxH-GO/N+M operates on the principle that CN- inhibits the catalytic activity of CoOxH-GO towards the H2O2-mediated oxidation of AR to form reddish resorufin on the membrane. The intensity of the red color of the membrane decreases with increasing CN- concentration, which can be easily observed with the naked eye at the nanomolar level. This cost-effective sensing system allows for the rapid and simple determination of the concentrations of CN- in complicated wastewater samples.

Metal-deposited bismuth oxyiodide nanonetworks with tunable enzyme-like activity: sensing of mercury and lead ions

In this study, we demonstrate that the enzyme-like activity of bismuth oxyiodide (BiOI) nanonetworks can be regulated through homogeneous deposition of metal atoms/ions or nanoparticles. Bismuth oxyhalide (BiOX; X = Cl, Br or I) nanostructures were prepared from a simple mixture of bismuth ions (Bi3+) and halide ions (X−) in aqueous solution. The BiOI nanonetworks exhibited much stronger (>25-fold) peroxidase-like activity than BiOCl or BiOBr nanosheets. In situ formation and deposition of gold nanoparticles (Au NPs) onto BiOI nanonetworks greatly enhanced the oxidase-like activity of the nanocomposites. The deposition of Ni, Zn or Mn on the BiOI nanonetworks boosted their peroxidase-like activity by at least 3-fold. Moreover, the catalase-like activity of the BiOI nanonetworks was elevated after deposition of MnO2 or ZnO nanoparticles. The enzyme-like activity of BiOI regulated by the deposition of metals was mainly due to the changes in the electronic and band structures of the BiOX nanonetworks, and the existence of surface metal atoms/ions in various oxidation states. We used the Au NPs/BiOI nanocomposites and NiO NPs/BiOI nanocomposites for the detection of Hg2+ and Pb2+ heavy metal ions, respectively, based on the suppression of the enzyme-like activity of the nanocomposite after deposition of these metal ions. These BiOI nanocomposite-based probes allow the selective detection of Hg2+ and Pb2+ down to nanomolar quantities. The practicality of these two nanozyme probes was validated by analysis of Hg2+ and Pb2+ ions in environmental water samples (tap water, river water, lake water, and sea water).

Reborn from the Ashes: Turning Organic Molecules to Antimicrobial Carbon Quantum Dots

Using polyamines as the initial organic raw material and by applying simple pyrolysis methods, super cationic carbon quantum dots (CQDs) can easily be made. Since polyamines are natural products and the synthesis procedure is green, these polyamine-derived CQDs display low toxicity and high biocompatibility but possess high antibacterial activity. In addition, polyamine-derived CQDs display other unique properties, such as facilitation of wound healing and passage through the tight junction, which make them a very promising bactericide in future clinical applications.

The Controversial Orientation of Adenine on Gold and Silver

In which orientation does adenine adsorb on gold and silver surfaces? This question has been a matter of debate for over 30 years. Since the dawn of surface-enhanced Raman spectroscopy (SERS); it and other techniques such as tip-enhanced Raman spectroscopy (TERS), surface-enhanced infrared absorption spectroscopy (SEIRAS), scanning tunneling microscopy (STM), density functional theory (DFT) simulations, and more, have been used in many attempts to answer this seemingly straightforward, yet controversial, question. Herein, the timeline and recent advances on this topic are explored, and the frequently contradictory findings are put into context and discussed.

Satellite-like Gold Nanocomposites for Targeted Mass Spectrometry Imaging of Tumor Tissues

We have developed a simple, rapid, high-throughput cancer diagnosis system using functional nanoparticles (NPs) consisting of poly(catechin) capped-gold NPs (Au@PC NPs) and smaller nucleolin-binding aptamer (AS1411) conjugated gold NPs (AS1411-Au NPs). The AS1411-Au NPs/Au@PC NP is used as a targeting agent in laser desorption/ionization mass spectrometry (LDI-MS)-based tumor tissue imaging. Self-assembled core-shell Au@PC NPs are synthesized by a simple reaction of tetrachloroaurate(III) with catechin. Au@PC NPs with a well-defined and dense poly(catechin) shell (~40-60 nm) on the surface of each Au core (~60-80 nm) are obtained through careful control of the ratio of catechin to gold ions, as well as the pH of the reaction solution. Furthermore, we have shown that AS1411-conjugated Au NPs (13-nm) self-assembled on Au@PC NP can from a satellite-like gold nanocomposite. The high density of AS1411-Au NPs on the surface of Au@PC NP enhances multivalent binding with nucleolin molecules on tumor cell membranes. We have employed LDI-MS to detect AS1411-Au NPs/Au@PC NPs labeled nucleolin-overexpressing MCF-7 breast cancer cells through the monitoring of Au cluster ions ([Aun]+; 1 ≤ n ≤ 3). The ultrahigh signal amplification from Au NPs through the formation of a huge number of [Aun]+ ions results in a sensing platform with a limit of detection of 100 MCF-7 cells mL-1. Further, we have applied the satellite-like AS1411-Au NPs/Au@PC NP nanocomposite as a labeling agent for tumor tissue imaging by LDI-MS. Our nanocomposite-assisted LDI-MS imaging platform can be extended for simultaneous analysis of different tumor markers on cell membranes when using different ligand-modified metal nanoparticles.

DNA Modulates the Interaction of Genetically Engineered DNA-Binding Proteins and Gold Nanoparticles: Diagnosis of High-Risk HPV Infection

Gene detection has an important role in diagnosing several serious diseases and genetic defects in modern clinical medicine. Herein, we report a fast and convenient gene detection method based on the modulation of the interaction between a heat-resistant double-stranded DNA (dsDNA)-binding protein (Sso7d) and gold nanoparticles (Au NPs). We prepared a recombinant Cys-Sso7d, which is Sso7d with an extra cysteine (Cys) residue in the N-terminus, through protein engineering to control the interaction between Sso7d and Au NPs. Cys-Sso7d exhibited a stronger affinity for Au NPs and more easily induced the aggregation of Au NPs than Sso7d. In addition, Cys-Sso7d retained its ability to bind with dsDNA. The aggregation of Au NPs induced by Cys-Sso7d was diminished in the presence of dsDNA, which could be utilized as a transduction mechanism for the detection of the polymerase chain reaction (PCR) products of human papillomavirus (HPV) gene fragments (HPV types 16 and 18). The Cys-Sso7d/Au NP probe could detect as few as 1 copy of the HPV gene. The sensitivity and specificity of the Cys-Sso7d/Au NP probe for Pap smear clinical specimens (n = 52) for HPV 16 and HPV 18 detection were 85.7%/100.0% and 85.7%/91.7%, respectively. Our results demonstrate that the Cys-Sso7d/Au NP probe can be used to diagnose high-risk HPV types in Pap smear samples with high sensitivity, specificity, and accuracy.