Yinglong Feng

Magnetoresistive performance and comparison of supermagnetic nanoparticles on giant magnetoresistive sensor-based detection system

Giant magnetoresistive (GMR) biosensors have emerged as powerful tools for ultrasensitive, multiplexed, real-time electrical readout, and rapid biological/chemical detection while combining with magnetic particles. Finding appropriate magnetic nanoparticles (MNPs) and its influences on the detection signal is a vital aspect to the GMR bio-sensing technology. Here, we report a GMR sensor based detection system capable of stable and convenient connection, and real-time measurement. Five different types of MNPs with sizes ranging from 10 to 100 nm were investigated for GMR biosensing. The experiments were accomplished with the aid of DNA hybridization and detection architecture on GMR sensor surface. We found that different MNPs markedly affected the final detection signal, depending on their characteristics of magnetic moment, size, and surface-based binding ability, etc. This work may provide a useful guidance in selecting or preparing MNPs to enhance the sensitivity of GMR biosensors, and eventually lead to a versatile and portable device for molecular diagnostics.

Magnetic Detection of Mercuric Ion Using Giant Magnetoresistance-Based Biosensing System

We have demonstrated a novel sensing strategy employing a giant magnetoresistance (GMR) biosensor and DNA chemistry for the detection of mercuric ion (Hg(2+)). This assay takes advantages of high sensitivity and real-time signal readout of GMR biosensor and high selectivity of thymine-thymine (T-T) pair for Hg(2+). The assay has a detection limit of 10 nM in both buffer and natural water, which is the maximum mercury level in drinking water regulated by U.S. Environmental Protection Agency (EPA). The magnitude of the dynamic range for Hg(2+) detection is up to three orders (10 nM to 10 μM). Herein, GMR sensing technology is first introduced into a pollutant monitoring area. It can be foreseen that the GMR biosensor could become a robust contender in the areas of environmental monitoring and food safety testing.

Giant magnetoresistive-based biosensing probe station system for multiplex protein assays

In this study, a sensitive immune-biosensing system capable of multiplexed, real-time electrical readout was developed based on giant magnetoresistive (GMR) sensor array to detect a panel of protein biomarkers simultaneously. PAPP-A, PCSK9, and ST2 have been regarded as promising candidate biomarkers for cardiovascular diseases. Early detection of multiple biomarkers for a disease could enable accurate prediction of a disease risk. 64 nano-size GMR sensors were assembled onto one 16 mm × 16 mm chip with a reaction well, and they could work independently and be monitored simultaneously. A detect limit of 40 pg/mL for ST2 antigen had been achieved, and the dynamic ranges for the three proteins detection were up to four orders of magnitude. The GMR sensing platform was also selective enough to be directly used in serum samples. In addition, a lab-based probe station has been designed to implement quick lab-on-a-chip experiments instead of wire bonding. It has a potential application in clinical biomarkers identification and screening, and can be extended to fit other biosensing schemes.

Surface Modification for Protein and DNA Immobilization onto GMR Biosensor

Giant magnetoresistance (GMR) biosensor with 20 nm SiO 2 on surface was successfully modified by 3-aminopropyltriethoxy silane (APTES) and glutaraldehyde (Glu). The resultant functionalized surface with terminal aldehyde groups was able to efficiently capture Interleukin-6 (IL-6) antibody and amine modified DNA (deoxyribonucleic acid) oligonucleotide. The immobilized IL-6 antibody could bind to IL-6 antigen, and fluorescence sandwich assay was demonstrated. The immobilized DNA could also hybridize with complementary DNA oligonucleotide. Streptavidin labeled magnetic nanoparticles with a diameter of 30 nm were both successfully bound to IL-6 antibody and DNA immobilized GMR biosensors after their respective sandwich binding and complementary hybridization. This APTES-Glu modification method could be also applicable to other surface for protein and DNA microarrays.

Superparamagnetic nanoparticle-based viscosity test

Hyperviscosity syndrome is triggered by high blood viscosity in the human body. This syndrome can result in retinopathy, vertigo, coma, and other unanticipated complications. Serum viscosity is one of the important factors affecting whole blood viscosity, which is regarded as an indicator of general health. In this letter, we propose and demonstrate a Brownian relaxation-based mixing frequency method to test human serum viscosity. This method uses excitatory and detection coils and Brownian relaxation-dominated superparamagnetic nanoparticles, which are sensitive to variables of the liquid environment such as viscosity and temperature. We collect the harmonic signals produced by magnetic nanoparticles and estimate the viscosity of unknown solutions by comparison to the calibration curves. An in vitro human serum viscosity test is performed in less than 1.5 min.

Localized detection of reversal nucleation generated by high moment magnetic nanoparticles using a large-area magnetic sensor

This report introduces a local-magnetic-reversal-nucleation based giant magnetoresistance (GMR) sensor with a large sensing area and further discusses its novel sensing scheme of high magnetic moment nanoparticles (MNPs). We demonstrated experimentally that this large-area GMR sensor could successfully detect high moment MNPs. The detection scheme of localized reversal nucleation of GMR sensor induced by MNPs was analyzed and further confirmed by the micromagnetic simulations. This work may provide one pathway in designing next generation GMR biosensors with large area and high sensitivity. This sensing scheme could be applicable to other magnetic biosensors such as magnetic tunnel junction sensors and planar Hall sensors.

Viscosity effect on the brownian relaxation based detection for immunoassay applications

Magnetic nanoparticles (MNPs) coated with Protein-G have been a model system to be used in different antibodies binding study. It is highly desirable to use a substrate-free biosensing system to detect antibodies binding in real-time. In this paper, we developed and applied a MNPs and search-coils integrated detection system, which is not only sensitive to the hydrodynamic volume of MNPs but also sensitive to the environment of MNPs, such as viscosity and temperature of the solution. We demonstrated that the viscosity effect influenced the amplitudes and phases of the 3rd (fH±2fL) and 5th (fH±4fL) harmonics for the mixed frequency testing scheme. The binding between antibodies and Protein-G on MNPs increased hydrodynamic volume of particles, as a result, it also changed the amplitudes and phases of harmonics, which are the object signals we need to analyze. We demonstrated that the viscosity of antibody solution is lower than that of MNP solution, and the antibody binding effect could be shielded by the viscosity effect to certain extent.

In Vitro Viscosity Measurement on Superparamagnetic Nanoparticle Suspensions

In this paper, we propose and demonstrate a Brownian relaxation-based mixing-frequency method to test sample viscosities. This method uses excitatory and detection coils and Brownian relaxation-dominated superparamagnetic nanoparticles, which are sensitive to the characteristics of the liquid environment such as viscosity. Oscillating magnetic fields can induce harmonics through the nonlinear magnetization curve of superparamagnetic nanoparticles. Phase lag of the third-harmonic signal and the induced voltage ratio of the fifth over the third harmonic signals are collected. We build up standard graphs by plotting collected data from eight magnetic nanoparticle (MNP) mixtures with different viscosities. For any unknown liquids mixed with MNPs, we can collect phase lag and voltage ratio information and insert these data into the aforementioned standard graphs. This in vitro viscosity test can be done in 1 min. Our experimental result showed a 0.3% error rate for the liquid viscosity test.