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The development of ultra-small platinum nanoparticles is very important for the sensitive detection of glucose in complex medium without protein interference. Zwitterionic dendrimer-encapsulated platinum nanoparticles (Ptn-G5MC NPs) have been developed and studied for the highly sensitive and selective colorimetric detection of glucose. Firstly, zwitterionic dendrimer (G5MC) was obtained by surface modification of generation 5 poly(amidoamine) dendrimer with maleic anhydride and cysteamine. The calculated average diameters of Pt nanoparticles (Pt NPs) for Ptn-G5MC (n = 55, 110, and 165) were 1.64 ± 0.22, 2.09 ± 0.24, and 2.98 ± 0.29 nm, respectively. Ptn-G5MC NPs not only had high stability in various pH solutions and fibrinogen solutions, but also showed no noticeable cytotoxicity against HUVEC cells and HeLa cells. In addition, Ptn-G5MC NPs catalyzed oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) with H2O2 to generate blue oxidized TMB (oxTMB), indicating their peroxidase-like property. This peroxidase-like reaction followed a typical Michaelis–Menten kinetics. Furthermore, this colorimetric reaction was used for glucose detection with high sensitivity and selectivity. The linear range of glucose concentration with absorbance at 652 nm was from 7 to 1380 μM, and the detection limit was 2.8 μM. More importantly, the relative activity of Ptn-G5MC NPs was not affected by proteins. These enhanced properties are attributed to the ultra-small size of Pt NPs and high stability of Pt55-G5MC NPs in complex medium. The glucose concentration in saliva as a real sample was found to be 0.18 mM. The proposed glucose sensor could have promising applications for glucose detection in biocatalysis and bioassays in the future.

The development of stable and biocompatible palladium nanoparticles (Pd NPs) catalysts has been drawing great interest. In this study, Pd NPs were prepared through a green method, where jujube polysaccharide (JP) was employed as both reducing and stabilizing agents for the first time. The JP stabilized palladium nanoparticles (Pdn-JP NPs) displayed small size, high stability, good biocompatibility and excellent catalytic efficiency. Pd50-JP NPs showed high stability up to two weeks in solutions of a wide pH range (4–9). Pd50-JP NPs showed negligible cytotoxicity against HeLa cells at a high concentration of up to 400 μg mL−1. Furthermore, Pdn-JP NPs showed excellent catalytic activity for reduction of 4-nitrophenol (4-NP) in the presence of sodium borohydride (NaBH4). The normalized rate constant (knor) and turnover frequency (TOF) of Pd50-JP NPs were as high as 38.4 s−1 mM−1 and 4455 h−1, respectively. The prepared Pdn-JP NPs will have various potential applications in bio-related catalysis in the future.

The development of monodisperse platinum nanoparticles with high biocompatibility for organic dye treatment has been drawing great interest. Herein, bovine serum albumin (BSA) was used to stabilize different platinum nanoparticles (Ptn@BSA NPs, n = 10, 15, and 20), where the Pt metal precursor (K2PtCl4) was incubated with BSA solution, followed by the addition of excess NaBH4 as a reducing agent. The prepared Ptn@BSA NPs had small size with a narrow distribution. They also showed good catalytic activity towards morin. Transmission electron microscopy (TEM) images demonstrated that the average sizes of Pt10@BSA, Pt15@BSA and Pt20@BSA were 1.70 ± 0.39, 2.15 ± 0.42 and 3.11 ± 0.72 nm, respectively. Dynamic light scattering (DLS) results showed that the hydrodynamic sizes of Pt10@BSA, Pt15@BSA and Pt20@BSA were 4.25, 6.57 and 8.84 nm, and the corresponding zeta potentials were −31.23, −30.20 and −29.77 mV, respectively. In addition, the oxidation of morin using Ptn@BSA NPs followed a pseudo-first-order reaction in the presence of H2O2. The apparent rate constant Kapp was dependent on the concentration of Ptn@BSA NPs, morin and H2O2. Ptn@BSA NPs expedited the formation of hydroxyl radicals (˙OH) from H2O2. More importantly, Ptn@BSA NPs were highly biocompatible towards HeLa cells. Taken together, Ptn@BSA could be employed as an eco-friendly catalyst to treat organic dyes in the future.

The development of artificial enzymes to mimic the properties of natural enzymes has been receiving much research interest. Herein, zwitterionic dendrimer-encapsulated palladium nanoparticles (Pdn-G5MC NPs) were constructed to investigate their biocompatibility and catalytic ability in bacterial solution. Zwitterionic dendrimer templates were synthesized via the surface modification of generation 5 polyamidoamine (G5 PAMAM) dendrimers with maleic anhydride and cysteamine. The Pdn-G5MC NPs were prepared by incubation of the templates with disodium tetrachloropalladate, followed by reduction with sodium borohydride. The Pdn-G5MC NPs displayed high stability, biocompatibility, and catalytic efficiency. Remarkably, Pd55-G5MC NPs maintained high stability over a broad pH range (4–9) and high salt concentration (up to 20%) within 24 h. Pd55-G5MC NPs did not show noticeable cytotoxicity to HUVEC cells or HeLa cells at a concentration of 500 μg mL−1, while G5 PAMAM dendrimer-encapsulated palladium nanoparticles (Pd55-G5 NPs) had obvious cytotoxicity (∼10% cell viability). Furthermore, Pd55-G5 NPs had a minimal inhibitory concentration (MIC) of 400 μg mL−1, while Pdn-G5MC NPs did not show any bacterial growth inhibition at the same concentration. More importantly, Pd55-G5MC NPs maintained their catalytic activity in bacterial solution compared to Pd55-G5 NPs. The apparent rate constant kapp is dependent on the concentration of morin or hydrogen peroxide. All the forementioned properties suggested that Pdn-G5MC NPs could be employed in bio-related systems in nature.

The development of stable and biocompatible gold nanoparticles has been drawing great interest. Dendrimers could be used as templates to entrap gold nanoparticles. Herein, dendrimer templates were prepared by the modification of generation 5 polyamidoamine (G5 PAMAM) dendrimers with maleic anhydride and cysteamine. Then modified dendrimer-encapsulated gold nanoparticles (Au-G5MC NPs) were formed by incubation of the templates with chloroauric acid and reduction with sodium borohydride. The resulting Au-G5MC NPs showed high stability, biocompatibility, and catalytic efficiency in water, which is ascribed to the single zwitterionic layer composed of amine and carboxyl groups. The single zwitterionic layer was shown to provide the Au-G5MC NPs with excellent stability in both phosphate-buffered saline and fibrinogen solutions. The mixed solution of Au-G5MC NPs with fibrinogen remained stable within 24 h, while the mixed solution of G5 PAMAM dendrimer-entrapped gold nanoparticles (Au-G5 NPs) with fibrinogen formed obvious aggregates immediately. Au-G5MC NPs displayed little cytotoxicity (>90% cell viability) against HeLa cells up to 100 μg mL−1, while Au-G5 NPs showed obvious cytotoxicity (60% cell viability). In addition, Au-G5MC NPs displayed high catalytic efficiency for the reduction reaction of 4-nitrophenol (4-NP) in water. This method can be used to prepare a variety of highly stable, biocompatible, and efficient dendrimer-encapsulated catalysts.