Chia-Lun Hsu

Synthesis of photoluminescent carbon dots for the detection of cobalt ions

We have developed a simple assay for the sensing of cobalt ions (Co2+), based on the analyte induced photoluminescence (PL) quenching of carbon dots (C-dots). The C-dots (mean diameter 3.6 ± 0.3 nm) prepared from L-cysteine through a simple hydrothermal process at 300 °C for 2 h have a quantum yield of 13.2%. The C-dots have strong blue PL with a maximum PL intensity at 395 nm under an excitation wavelength of 325 nm. Through the reactions of Co2+ ions with cysteine molecules/residues on the surfaces of the C-dots, non-photoluminescent CoxSy nanoparticles are formed. As-formed CoxSy nanoparticles and the C-dots further form aggregates in the solution, leading to PL quenching. The C-dot probe allows detection of Co2+ ions over a concentration range from 10 nM to 100 μM (R2 = 0.992). This reliable, rapid, sensitive, and selective C-dot probe has been utilized for the determination of the concentrations of Co2+ ions in vitamin B12 and natural water samples.

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.

Highly flexible and stable aptamer-caged nanoparticles for control of thrombin activity

In this paper, we have demonstrated that the thymine linker length number (Tn, n = 0–60) and stem pair number (Pm, m = 0–16) in the terminal of thrombin binding aptamers (TBAs) have a strong impact on the flexibility and stability of TBA-modified gold nanoparticles (TBA–Au NPs) and thus the binding strength and inhibitory potency toward thrombin. The anticoagulation of TBA–Au NPs increased with an increase in the linker length from T0 to T30 due to an increase in the flexibility of G-quadruplexes of TBAs on the Au NP surfaces (TBA-Tn–Au NPs). The inhibition of TBA-PmT15–Au NPs increased with an increase in the Pm from P0 to P8 as a result of the increase in the rigidity and the stability of G-quadruplexes of the TBAs on the Au NP surfaces. The best results were observed for multivalent TBA–Au NPs conjugates—TBA15/TBA29-P8T15–Au NPs—which exhibited ultra-high binding affinity toward thrombin (Kd = 8.86 × 10−12 M) and thus extremely high anticoagulant (inhibitory) potency because of their particularly flexible and stable conformation and multivalency. Compared to the case without inhibitors, their measured thrombin clotting time (TCT) was 296 times longer, whereas for TBA15 alone it was only 3.9 times longer. From the dosage dependence of the TCT delay, we further demonstrated the anticoagulation ability of our TBA15/TBA29-P8T15–Au NPs was much better than the commercial drugs (argatroban and hirudin). Moreover, the Au NPs modified with TBA with photocleavable (PC) units allow a reversal in the activity of TBAPC–Au NPs via near-UV light-inducement of TBA release from Au NPs. We believe that our described techniques can be used widely to modify NPs with other anticoagulant DNA or RNA aptamers towards different proteins such as factor IX, activated protein C, and factor VIIa.

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).

Detection of adenosine triphosphate through polymerization-induced aggregation of actin-conjugated gold/silver nanorods

We have developed a simple and selective nanosensor for the optical detection of adenosine triphosphate (ATP) using globular actin-conjugated gold/silver nanorods (G-actin-Au/Ag NRs). By simply mixing G-actin and Au/Ag NRs (length ~56 nm and diameter ~12 nm), G-actin-Au/Ag NRs were prepared which were stable in physiological solutions (25 mM Tris-HCl, 150 mM NaCl, 5.0 mM KCl, 3.0 mM MgCl2 and 1.0 mM CaCl2; pH 7.4). Introduction of ATP into the G-actin-Au/Ag NR solutions in the presence of excess G-actin induced the formation of filamentous actin-conjugated Au/Ag NR aggregates through ATP-induced polymerization of G-actin. When compared to G-actin-modified spherical Au nanoparticles having a size of 13 nm or 56 nm, G-actin-Au/Ag NRs provided better sensitivity for ATP, mainly because the longitudinal surface plasmon absorbance of the Au/Ag NR has a more sensitive response to aggregation. This G-actin-Au/Ag NR probe provided high sensitivity (limit of detection 25 nM) for ATP with remarkable selectivity (>10-fold) over other adenine nucleotides (adenosine, adenosine monophosphate and adenosine diphosphate) and nucleoside triphosphates (guanosine triphosphate, cytidine triphosphate and uridine triphosphate). It also allowed the determination of ATP concentrations in plasma samples without conducting tedious sample pretreatments; the only necessary step was simple dilution. Our experimental results are in good agreement with those obtained from a commercial luciferin-luciferase bioluminescence assay. Our simple, sensitive and selective approach appears to have a practical potential for the clinical diagnosis of diseases (e.g. cystic fibrosis) associated with changes in ATP concentrations.

Analyses of functional polymer-modified nanoparticles for protein sensing by surface-assisted laser desorption/ionization mass spectrometry coupled with HgTe nanomatrices.

In this study, we employed HgTe nanostructure-based matrices (nanomartrices; NMs) for surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) for the analyses of polyethylene glycol (PEG) derivatives as well as thiol-PEG-modified gold nanoparticles (PEG-Au NPs). Relative to common organic matrices, the use of HgTe NMs as the matrix for SALDI-MS resulted in more highly efficient analyses of PEG derivatives, in terms of sensitivity and reproducibility. The symmetric MS profiles of PEG (Mw: ca. 8000 Da) obtained through HgTe NMs/SALDI-MS analysis revealed the absence of polymer degradation during this process. Under optimal conditions, the HgTe NMs/SALDI-MS system enabled the detection of PEG sample as low as 100 pg and with molecular weights of up to approximately 42,000 Da. We also used this approach for the analyses of PEG-Au NPs in which various functional groups (carboxymethyl, amine, biotin) were present at the PEG termini, revealing that the combination of SALDI-MS and HgTe NMs have great potential for use in the characterization of modified polymer-ligands on nanomaterials. We also demonstrated the PEG-Au NPs can be coupled with HgTe NMs/SALDI-MS for characterization of biorecognition events. After avidin, the target protein, had been selectively captured by the biotin-PEG-Au NPs, we found that the desorption/ionization efficiency of biotin-PEG from the Au NP surface was suppressed; accordingly, this novel SALDI-MS approach allows rapid detection of avidin with high specificity and sensitivity. Au NP surfaces functionalized with other functional-PEG ligands might also allow amplification of signals from other biological interactions.