Affinity Immobilization of a Bacterial Prolidase onto Metal-Ion-Chelated Magnetic Nanoparticles for the Hydrolysis of Organophosphorus Compounds

In this study, silica-coated magnetic nanoparticles (SiMNPs) with isocyanatopropyltriethoxysilane as a metal-chelating ligand were prepared for the immobilization of His6-tagged Escherichia coli prolidase (His6-EcPepQ). Under one-hour coupling, the enzyme-loading capacity for the Ni2+-functionalized SiMNPs (NiNTASiMNPs) was 1.5 mg/mg support, corresponding to about 58.6% recovery of the initial activity. Native and enzyme-bound NiNTASiMNPs were subsequently characterized by transmission electron microscopy (TEM), superparamagnetic analysis, X-ray diffraction, and Fourier transform infrared (FTIR) spectroscopy. As compared to free enzyme, His6-EcPepQ@NiNTASiMNPs had significantly higher activity at 70 °C and pH ranges of 5.5 to 10, and exhibited a greater stability during a storage period of 60 days and could be recycled 20 times with approximately 80% retention of the initial activity. The immobilized enzyme was further applied in the hydrolysis of two different organophosphorus compounds, dimethyl p-nitrophenyl phosphate (methyl paraoxon) and diethyl p-nitrophenyl phosphate (ethyl paraoxon). The experimental results showed that methyl paraoxon was a preferred substrate for His6-EcPepQ and the kinetic behavior of free and immobilized enzymes towards this substance was obviously different. Taken together, the immobilization strategy surely provides an efficient means to deposit active enzymes onto NiNTASiMNPs for His6-EcPepQ-mediated biocatalysis.

Magnetic Graphene Field-Effect Transistor Biosensor for Single-Strand DNA Detection

Herein, a magnetic graphene field-effect transistor biosensor was prepared through the transfer of a chemical vapor deposition graphene film onto a glass substrate to produce a sensing film and conductive channel. By fixing 1-pyrenebutanoic acid succinimidyl ester onto graphene film as an anchor, a probe aptamer was immobilized on the graphene film in order to capture magnetically labeled complementary single-stranded DNA. Our experiments showed that, within a periodic magnetic field, the biosensor impedance exhibited a periodic oscillation, the amplitude of which was correlated to the complementary DNA concentration. Based on this principle, the magnetic graphene field-effect transistor was utilized to detect single-stranded DNA with detection limition of 1 pM. The results were rationalized using a model wherein the magnetic force causes the DNA strand to bend, thereby resulting in magnetic nanobeads/DNA modulation of the double conductive layer of graphene transistors. Furthermore, since a periodic magnetic field could be introduced to produce a periodic impedance changes of MGFETs, sampling integration could be used to improve the signal-to-noise ratio efficiently by increasing the number of periods of the external magnetic field. Therefore, a novel biosensor for DNA detection with high sensitivity has been presented in this work. Based on the detection principle, this system may also be a potential tool for detecting other bio-molecules, cells, etc.

Progress of recyclable magnetic particles for biomedical applications

The preparation, types, recycling methods, biomedical applications and outlook of recyclable magnetic particles have been reviewed.

Ultrasensitive DNA detection based on two-step quantitative amplification on magnetic nanoparticles

Sensitive detection of a specific deoxyribo nucleic acid (DNA) sequence is important for biomedical applications. In this report, a two-step amplification strategy is developed based on magnetic nanoparticles (MNPs) to achieve ultrasensitive DNA fluorescence detection. The first level amplification is obtained from multiple binding sites on MNPs to achieve thousands of probe DNA molecules on one nanoparticle surface. The second level amplification is gained by enzymatic reaction to achieve fluorescence signal enhancement. MNPs functionalized by probe DNA (DNAp) are bound to target DNA (t-DNA) molecules with a ratio of 1:1 on a substrate with capture DNA (DNAc). After the MNPs with DNAp are released from the substrate, alkaline phosphatase (AP) is labelled to MNPs via hybridization reaction between DNAp on MNPs and detection DNAs (DNAd) with AP. The AP on MNPs catalyses non-fluorescent 4-methylumbelliferyl phosphate (4-MUP) to fluorescent 4-methylumbelliferone (4-MU) with high intensity. Finally, fluorescence intensity of the 4-MU is detected by a conventional fluorescence spectrophotometer. With this two-step amplification strategy, the limit of detection (LOD) of 2.8 × 10(-18) mol l(-1) for t-DNA has been achieved.