Magnetic nanozymes with peroxidase-mimicking activity have been widely investigated for developing molecular biosensors. Herein, we report a starch-assisted method for the synthesis of a novel class of carboxyl group-functionalized iron oxide nanoparticles (C-IONPs). Scanning electron and transmission electron microscopy analysis revealed that the nanoparticles possess a spherical shape with an average size of ∼250 nm. Peroxidase-mimicking activity of C-IONPs was investigated through catalytic oxidation of 3,3′,5,5′tetramethylbenzidine (TMB) in the presence of H 2 O 2 . The results showed that nanoparticles follow typical Michaelis−Menten kinetics and exhibit excellent affinity toward TMB and H 2 O 2 with estimated K M and V Max values of 0.0992 mM and 0.156 × 10 −8 Ms −1 for TMB and 114 mM and 0.197 × 10 −8 Ms −1 for H 2 O 2 , respectively. C-IONPs were used to develop a simple method for the direct isolation and quantification of disease-specific exosomes. This method utilized a two-step strategy that involved (a) initial isolation of bulk exosomes present in the sample media using tetraspanin biomarker (i.e., CD9)-functionalized C-IONPs and (b) subsequent electrochemical quantification of disease-specific exosomes within the captured bulk exosomes using tumor-specific markers (in this case, the ovarian cancer biomarker CA-125). In the first step, C-IONPs were used as "dispersible nanocarriers" to capture the bulk population of exosomes, and in the second step, they were used as nanozymes to generate an enzyme-catalyzed current indicative of the presence of tumor-specific exosomes. Chronoamperometric analysis showed that the method exhibits an excellent specificity for OVCAR3 cell-derived exosomes (linear dynamic range, 6.25 × 10 5 to 1.0 × 10 7 exosomes/mL; detection limit, 1.25 × 10 6 exosomes/mL) with a relative standard deviation of <5.0% (n = 3). Due to their excellent enzyme catalytic activity, ability to magnetically separate the target from bulk samples, and versatile bioconjugation capability (because of the −COOH group), C-IONPs are a promising candidate for the development of advanced exosome biosensing assays for various clinical applications.

This article reports on the peroxidase-like catalytic activity of polyoxometalates (POMs) and their potential use as natural peroxidases for developing a simple and efficient colorimetric glucose sensor. Two Keggin-type vanadium-substituted tungstosulfates, [SVW 11 O 40 ] 3À (SVW 11) and [SV 2 W 10 O 40 ] 4À (SV 2 W 10), were tested for their potential as natural enzyme mimetics and exhibited strong peroxidase-like catalytic activity. The catalysis reaction was found to be in accordance with Michaelis-Menten and Lineweaver-Burk kinetics models. Michaelis-Menten constant (K m) and maximum velocity (V max) parameters were calculated to be 0.0759 mM and 0.329 × 10 À 8 Ms À 1 for SVW 11 , and 0.0543 mM and 2.67 × 10 À 8 Ms À 1 for SV 2 W 10 , respectively, indicating a high catalytic activity and a strong affinity of POMs towards 3,3,5,5-tetramethylbenzidine (TMB). In the case of H 2 O 2 , these values were found to be 57.1 mM and 0.325 × 10 À 8 mMs À 1 for SVW 11 , and 47.7 mM and 2.72 × 10 À 8 mMs À 1 for SV 2 W 10. The peroxidase-like catalytic activity of these POMs was used to develop colorimetric glucose sensors as a proof-of-concept model for the POM-based naked-eye detection of biomolecules. The limit of detcetion (LOD) of glucose for SVW 11 and SV 2 W 10 was 1.14 μM and 1.24 μM, respectively. Our findings propose broad-ranging potential applications of these novel POMs in biosensing and bioanalytical chemistry.

Barium strontium titanate (BST) and iron doped barium strontium titanate (BSTF) ceramics with general formula (Ba 0.5 Sr 0.5 Ti 1-y Fe y O 3 ) and different iron (Fe) contents were prepared by slow rate injection sol-gel technique. The phase analysis, morphology and dielectric properties of BSTFs were investigated. The phase analysis was carried out using XRD which revealed the crystallization of BSTF in perovskite structure with single phase. The Fe doped BST peaks shifted toward higher angles and the calculated crystallite size was 19 nm on average. The BSTF morphology was studied using TEM which showed that the particle size was affected by Fe content. The average particle size was found to be 37 nm for (Ba 0.5 Sr 0.5 Ti 1-y Fe y O 3 ) with Fe concentration of (y = 0.01, 0.05 and 0.1) calcined at (600, 800 and 1000°C). The dielectric measurements were carried out using impedance analyzer at room temperature as a function of frequency in the range of 10 Hz to 1 MHz. The dielectric constant and dielectric loss of the 1 mol% Fe-doped Ba 0.5 Sr 0.5 TiO 3 at 1 kHz were 1453.69 and 0.0063, respectively. The BSTF ceramics with high dielectric constant and low dielectric loss were obtained for the application DRAM cell capacitor.

No abstract