Monodispersed, Micron-Sized Supermicroporous Silica Particles by Cetyltrimethylammonium Bromide-Mediated Preparation

In this study, we present a novel modified Stöber method utilizing cetyltrimethylammonium bromide (CTAB) as a mediator for the preparation of monodispersed, micron-sized supermicroporous silica particles. Observed results show prepared silica particles ranging in size from 0.64 to 1.36 μm with an increase in CTAB concentration from 1.0 to 5.0 mM. The particles exhibited low polydispersity (<5%), a high Brunauer–Emmett–Teller surface area (570 to 1064 m2/g), and pore volumes ranging from 0.22 to 0.39 cm3/g. The pore size, determined using the Barrett–Joyner–Halenda method from the adsorption branches of the isotherms, was approximately 1.9 nm, specifically 1.83, 1.85, and 1.90 nm, as the CTAB concentration increased from 1.0 to 2.5 and 5.0 mM, respectively. The resulting particles displayed a narrow distribution of pore diameters. In addition, to obtain an in-depth understanding of the role of CTAB on the preparation of silica particles, a possible mechanism is also investigated using conductivity, dynamic light scattering (DLS), zeta potential, FT-IR spectra, and transmission electron microscopy. Our findings demonstrate that CTAB plays multiple roles in the hydrolysis/condensation of TEOS (tetraethyl orthosilicate) and subsequent nucleation and growth of silica particles. CTAB acts as a template for superporosity, a stabilizer for colloids, and an accelerator for nucleation and growth, leading to formation of monodispersed micrometer silica particles. Further characterization through FT-IR and 29Si solid NMR spectra revealed that the micron silica particles were obtained with inhomogeneity in the condensation degree, allowing for selective etching through hot incubation to form micron-sized hollow silica spheres

Gold Nanoparticle-Based Facile Detection of Human Serum Albumin and Its Application as an INHIBIT Logic Gate

In this work, a facile colorimetric method is developed for quantitative detection of human serum albumin (HSA) based on the antiaggregation effect of gold nanoparticles (Au NPs) in the presence of HSA. The citrate-capped Au NPs undergo a color change from red to blue when melamine is added as a cross-linker to induce the aggregation of the NPs. Such an aggregation is efficiently suppressed upon the adsorption of HSA on the particle surface. This method provides the advantages of simplicity and cost-efficiency for quantitative detection of HSA with a detection limit of ∼1.4 nM by monitoring the colorimetric changes of the Au NPs with UV–vis spectroscopy. In addition, this approach shows good selectivity for HSA over various amino acids, peptides, and proteins and is qualified for detection of HSA in a biological sample. Such an antiaggregation effect can be further extended to fabricate an INHIBIT logic gate by using HSA and melamine as inputs and the color changes of Au NPs as outputs, which may have application potentials in point-of-care medical diagnosis

Self-Assembled Peptide Hydrogel as a Smart Biointerface for Enzyme-Based Electrochemical Biosensing and Cell Monitoring

A self-assembled peptide nanofibrous hydrogel composed of <i>N</i>-fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) was used to construct a smart biointerface. This biointerface was then used for enzyme-based electrochemical biosensing and cell monitoring. The Fmoc-FF hydrogel had two functions. One was as a matrix to embed an enzyme model, horseradish peroxidase (HRP), during the self-assembly of Fmoc-FF peptides. The other was use as a robust substrate for cell adhesion. Experimental data demonstrated that HRP was immobilized in a stable manner within the peptide hydrogel, and that HRP retained its inherent bioactivity toward H₂O₂. The HRP also can realize direct electron transfer in the Fmoc-FF hydrogel. The resulting third-generation electrochemical H₂O₂ biosensor exhibited good analytical performance, including a low limit of detection of 18 nM, satisfactory reproducibility, and high stability and selectivity. HeLa cells were then adhered to the HRP/Fmoc-FF hydrogel-modified electrode. The sensitive in situ monitoring of H₂O₂ released from HeLa cells was realized. This biointerface based on the Fmoc-FF hydrogel was easily prepared, environmentally friendly, and also versatile for integration of other cells and recognized molecules for the monitoring of various cellular biomolecules. The smart biointerface has potential application in broad physiological and pathological investigations

Boosting ORR Activity in π‑Rich Carbon-Supported Sub‑3 nm Pt-Based Intermetallic Electrocatalysts via d–π Interaction

Regulating Pt–C interactions is the key to improving the performance of carbon-supported Pt-based electrocatalysts. However, the surfaces of common commercial carbon supports are relatively inert, and achieving strong bonding with metals remains a challenge. Herein, a simple method is employed to prepare highly dispersed and sub-3 nm PtCo intermetallic compounds (IMCs) supported on π-electron-rich nitrogen-doped petroleum vacuum residue-derived porous carbon (NPPC) for the oxygen reduction reaction (ORR). Strong interaction between the d-orbitals of PtCo particles (NPs) and the π electrons of NPPC significantly optimizes the metal d-orbitals. Such strong d–π interaction and the synergistic effect of pyridinic N further enhance the activity of the catalyst for ORR. The mass activity (MA) of the prepared PtCo/NPPC-800 catalyst (1.77 A mgPt–1) is experimentally demonstrated to be 11.8 times higher than that of commercial Pt/C (0.15 A mgPt–1) at 0.9 V vs RHE. X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) spectra confirm the low degree of π-electron delocalization of NPPC and high-strength Pt–C bonding. This work greatly improves the high value-added utilization of heavy oil and also provides new insights into the preparation of small-sized Pt-based IMC catalysts for ORR

Dot–Wire–Platelet–Cube: Step Growth and Structural Transformations in CsPbBr₃ Perovskite Nanocrystals

While the classical mechanism for the growth of colloidal chalcogenide nanocrystals is largely understood, fundamental insights for the growth of perovskite nanocrystals still remain elusive. Using nanoclusters of ∼0.6 nm diameter as monomers and growing to more than 25 nm in a single reaction, herein, the step growth process of perovskite CsPbBr₃ nanocrystals is reported. This is performed with a step-rise of the reaction temperature with correlating annealing time. The growth is so precise that ∼0.6 nm (nearly one unit cell) increments were successively monitored in parallel with the conversion of clusters to nanowires and then to thickness tunable platelets and finally to size-tunable cube-shaped nanostructures. The entire reaction was monitored optically and microscopically, and their step growths were correlated. From these observations, the possible growth mechanism for perovskite nanocrystals along with their shape transformations was proposed

Citrate-Regulated Surface Morphology of SiO₂@Au Particles To Control the Surface Plasmonic Properties

In this work, SiO₂@Au core–shell particles under ambient conditions were prepared by using 120 nm SiO₂ spheres with ca. 4 nm Au nanoparticles decorated on the surfaces as seeds, the aqueous solutions of sodium citrate/HAuCl₄ mixtures as growth solutions, and hydroxylamine as reducing agent. The morphology of the Au shells obtained on the SiO₂ spheres was readily regulated only by the citrate-to-HAuCl₄ molar ratio; no deliberate adjustment of the temperature and pH of the reaction media was needed. When the citrate-to-HAuCl₄ molar ratio in the growth solution was below 4:1, the surfaces of the SiO₂ spheres were covered with sparsely packed Au nanoparticles with sizes in the range of 20–40 nm, depending on the citrate-to-HAuCl₄ molar ratio. When the citrate-to-HAuCl₄ molar ratio in the growth solution was above 8:1, the surfaces of the SiO₂ spheres were coated by complete, uniform Au nanoshells. Concomitant with this citrate-regulated morphology, the localized surface plasmon resonance peaks of the resulting SiO₂@Au particles shifted from 611 nm for the sparse Au nanoparticle coating to 784 nm for the complete Au nanoshell coating. Furthermore, the sparsely packed Au nanoparticle coating showed stronger surface enhancement Raman spectroscopic signals than the uniform Au nanoshell coating, while the latter exhibit higher photothermal efficiency than the former

Turn-on Fluorescent InP Nanoprobe for Detection of Cadmium Ions with High Selectivity and Sensitivity

We reported a “turn-on” fluorescent InP nanoprobe for detection of cadmium ions in hydrophobic and hydrophilic media. The method based on the turn-on fluorescence detection of cadmium ions has shown its high selectivity and sensitivity, which are independent of the pH of the tested samples. Also, this approach exhibits an immediate response to cadmium ions, and visualized detection of cadmium ions has further been demonstrated under a UV lamp

Seamless Signal Transduction from Three-Dimensional Cultured Cells to a Superoxide Anions Biosensor via In Situ Self-Assembly of Dipeptide Hydrogel

This study demonstrates a new strategy for the development of a three-dimensional (3D) cell culture model-based cellular biosensing system. Distinctly different from the previously reported layering or separating fabrication of cell culture and sensing devices, herein living cells and enzymes as sensing elements are immobilized into a dipeptide-derived hydrogel matrix through simple one-pot self-assembly. The cells are then 3D cultured in the functional hydrogel, and the releasing superoxide anion (O₂^•–) is detected in situ by a cascade superoxide dismutase and horseradish peroxidase-based electrochemical biosensor. This novel design provides considerable advantages, including the possibility of capturing molecular signals immediately after they are secreted from living cells, due to the close proximity of the enzymes and the O₂^•–-producing cells. Furthermore, incorporating all components in a 3D matrix provides a confinement environment, that can lead to a concentrating effect of analysts. These properties allow the sensing device to achieve ultrahigh sensitivity and a precise response to a very low number of O₂^•– molecules. The proposed approach, based on the self-assembly of a small molecular hydrogel, also simplifies experimental procedures and increases protocol flexibility to cell culture methodology and sensing design. Consequently, this novel 3D culture model-based cellular biosensing system is envisaged to be useful for cellular function and pathology, drug discovery, and toxicity studies

Syntheses and Characterization of Nearly Monodispersed, Size-Tunable Silver Nanoparticles over a Wide Size Range of 7–200 nm by Tannic Acid Reduction

Nearly monodispersed spherical silver nanoparticles (Ag NPs) were synthesized by using tannic acid (TA) as both reductant and stabilizer in a 30 °C water bath. The size of the as-prepared Ag NPs could be tuned in a range of 7–66 nm by changing the molar ratio of TA to silver nitrate and pH of the reaction solutions. UV–vis spectra, TEM observations, and temporal evolution of the monomer concentrations for the reactions carried out at different experimental conditions showed that the improved size distribution and size tunability of the Ag NPs were mainly attributed to the use of TA, which could promote the balance of nucleation and growth processes of the NPs effectively. The size of the Ag NPs was extendable up to 200 nm in one-pot fashion by the multi-injection approach. The size-dependent surface-enhanced Raman scattering (SERS) activity of the as-prepared Ag NPs was evaluated, and the NPs with size around 100 nm were identified to show a maximum enhanced factor of 3.6 × 10⁵. Moreover, the as-prepared TA-coated Ag NPs presented excellent colloidal stability compared to the conventional citrate-coated ones

Turn-on Fluorescent InP Nanoprobe for Detection of Cadmium Ions with High Selectivity and Sensitivity

We reported a “turn-on” fluorescent InP nanoprobe for detection of cadmium ions in hydrophobic and hydrophilic media. The method based on the turn-on fluorescence detection of cadmium ions has shown its high selectivity and sensitivity, which are independent of the pH of the tested samples. Also, this approach exhibits an immediate response to cadmium ions, and visualized detection of cadmium ions has further been demonstrated under a UV lamp