Magnetoresistive biosensors with on-chip pulsed excitation and magnetic correlated double sampling

Sandwich Immunosensor Based on Particle Motion: How Do Reactant Concentrations and Reaction Pathways Determine the Time-Dependent Response of the Sensor?

To control and optimize the speed of a molecular biosensor, it is crucial to quantify and understand the mechanisms that underlie the time-dependent response of the sensor. Here, we study how the kinetic properties of a particle-based sandwich immunosensor depend on underlying parameters, such as reactant concentrations and the size of the reaction chamber. The data of the measured sensor responses could be fitted with single-exponential curves, with characteristic response times that depend on the analyte concentration and the binder concentrations on the particle and substrate. By comparing characteristic response times at different incubation configurations, the data clarifies how two distinct reaction pathways play a role in the sandwich immunosensor, namely, analyte binding first to particles and thereafter to the substrate, and analyte binding first to the substrate and thereafter to a particle. For a concrete biosensor design, we found that the biosensor is dominated by the reaction pathway where analyte molecules bind first to the substrate and thereafter to a particle. Within this pathway, the binding of a particle to the substrate-bound analyte dominates the sensor response time. Thus, the probability of a particle interacting with the substrate was identified as the main direction to improve the speed of the biosensor while maintaining good sensitivity. We expect that the developed immunosensor and research methodology can be generally applied to understand the reaction mechanisms and optimize the kinetic properties of sandwich immunosensors with particle labels.

Highly stable integration of graphene Hall sensors on a microfluidic platform for magnetic sensing in whole blood

The detection and analysis of rare cells in complex media such as blood is increasingly important in biomedical research and clinical diagnostics. Micro-Hall detectors (μHD) for magnetic detection in blood have previously demonstrated ultrahigh sensitivity to rare cells. This sensitivity originates from the minimal magnetic background in blood, obviating cumbersome and detrimental sample preparation. However, the translation of this technology to clinical applications has been limited by inherently low throughput (<1 mL/h), susceptibility to clogging, and incompatibility with commercial CMOS foundry processing. To help overcome these challenges, we have developed CMOS-compatible graphene Hall sensors for integration with PDMS microfluidics for magnetic sensing in blood. We demonstrate that these graphene μHDs can match the performance of the best published μHDs, can be passivated for robust use with whole blood, and can be integrated with microfluidics and sensing electronics for in-flow detection of magnetic beads. We show a proof-of-concept validation of our system on a silicon substrate and detect magnetic agarose beads, as a model for cells, demonstrating promise for future integration in clinical applications with a custom CMOS chip.

From saliva to SNP: non-invasive, point-of-care genotyping for precision medicine applications using recombinase polymerase amplification and giant magnetoresistive nanosensors

Genetic testing is considered a cornerstone of the precision medicine paradigm. Genotyping of single nucleotide polymorphisms (SNPs) has been shown to provide insights into several important issues, including therapy selection and drug responsiveness. However, a scarcity of widely deployable and cost-effective genotyping tools has limited the integration of precision medicine into routine clinical practice. The objective of our work was to develop a portable, cost-effective, and automated platform that performs SNP genotyping at the point-of-care (POC). Using recombinase polymerase amplification (RPA) and giant magnetoresistive (GMR) nanosensors, we present a highly automated and multiplexed point-of-care platform that utilizes direct saliva for the qualitative genotyping of four SNPs (rs4633, rs4680, rs4818, rs6269) along the catechol-O-methyltransferase gene (COMT), which is associated with the modulation of pain sensitivity and perioperative opioid use. Using this approach, we successfully amplify, detect, and genotype all four of the SNPs, demonstrating 100% accordance between the experimental results obtained using the automated RPA and GMR genotyping assay and the results obtained using a COMT PCR genotyping assay that was formerly validated using pyrosequencing. This automated, portable, and multiplexed RPA and GMR assay shows great promise as a solution for SNP genotyping at the POC and reinforces the broad applications of magnetic nanotechnology in biomedicine.

An automated and mobile magnetoresistive biosensor system for early hepatocellular carcinoma diagnosis

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related deaths worldwide. Most patients, however, are not diagnosed until advanced stage because early HCC lesions generally cause no overt symptoms, and the presence of cirrhosis adds another layer of complexity. While early diagnosis enables more therapeutic options and greatly improves survival rates, it is difficult to achieve. In order to detect early stage HCC, high-risk patients need to frequently measure serum biomarkers such as alpha-fetoprotein (AFP), and gold standards for detection involve less accessible and costly tests. In this work, we present an automated and mobile magnetoresistive biosensor system that allows quick, easy, and accurate detection of a panel of HCC related biomarkers. We first discuss the underlying principles of the giant magnetoresistive (GMR) biosensor system and its unique advantages in early detection of HCC. We also describe the development of hardware, software, and the bioassay, and demonstrate that it can perform an automated assay in 28 min, providing both qualitative and quantitative results. The user only needs to manually add sample into a disposable cartridge and press a button on the smartphone app, without the need for direct interaction with reagent liquids, or lab skills such as pipetting. With its portability, high sensitivity, and ease-of-use, the presented biosensor system has the potential to empower both medical practitioners and patients to achieve early HCC diagnosis. Furthermore, the GMR biosensor platform can be adapted to detect other protein or DNA biomarkers beyond HCC, bringing the goals of accessible mobile health even closer to reality.

The Challenges of Developing Biosensors for Clinical Assessment: A Review

Emerging research in biosensors has attracted much attention worldwide, particularly in response to the recent pandemic outbreak of coronavirus disease 2019 (COVID-19). Nevertheless, initiating research in biosensing applied to the diagnosis of diseases is still challenging for researchers, be it in the preferences of biosensor platforms, selection of biomarkers, detection strategies, or other aspects (e.g., cutoff values) to fulfill the clinical purpose. There are two sides to the development of a diagnostic tool: the biosensor development side and the clinical side. From the development side, the research engineers seek the typical characteristics of a biosensor: sensitivity, selectivity, linearity, stability, and reproducibility. On the other side are the physicians that expect a diagnostic tool that provides fast acquisition of patient information to obtain an early diagnosis or an efficient patient stratification, which consequently allows for making assertive and efficient clinical decisions. The development of diagnostic devices always involves assay developer researchers working as pivots to bridge both sides whose role is to find detection strategies suitable to the clinical needs by understanding (1) the intended use of the technology and its basic principle and (2) the preferable type of test: qualitative or quantitative, sample matrix challenges, biomarker(s) threshold (cutoff value), and if the system requires a mono- or multiplex assay format. This review highlights the challenges for the development of biosensors for clinical assessment and its broad application in multidisciplinary fields. This review paper highlights the following biosensor technologies: magnetoresistive (MR)-based, transistor-based, quartz crystal microbalance (QCM), and optical-based biosensors. Its working mechanisms are discussed with their pros and cons. The article also gives an overview of the most critical parameters that are optimized by developing a diagnostic tool.

A CMOS Magnetoresistive Sensor Front-End With Mismatch-Tolerance and Sub-ppm Sensitivity for Magnetic Immunoassays

Magnetic biosensing is an emerging technique for ultra-sensitive point-of-care (PoC) biomolecular detection. However, the large baseline-to-signal ratio and sensor-to-sensor mismatch in magnetoresistive (MR) biosensors severely complicates the design of the analog front-end (AFE) due to the high dynamic range (DR) required. The proposed AFE addresses these issues through new architectural and circuit level techniques including fast settling duty-cycle resistors (DCRs) to reduce readout time and a high frequency interference rejection (HFIR) sampling technique embedded in the ADC to relax the DR requirement. The AFE achieves an input-referred noise of 46.4 nT/√Hz, an input-referred baseline of less than 0.235 mT, and a readout time of 11 ms while consuming just 1.39 mW. Implemented in a 0.18 μm CMOS process, this work has state-of-the-art performance with 22.7× faster readout time, >7.8× lower baseline, and 2.3× lower power than previously reported MR sensor AFEs.

National Cancer Institute Alliance for nanotechnology in cancer-Catalyzing research and translation toward novel cancer diagnostics and therapeutics

Nanotechnology has been a burgeoning research field, which is finding compelling applications in several practical areas of everyday life. It has provided novel, paradigm shifting solutions to medical problems and particularly to cancer. In order to accelerate integration of nanotechnology into cancer research and oncology, the National Cancer Institute (NCI) of the National Institutes of Health (NIH) established the NCI Alliance for Nanotechnology in Cancer program in 2005. This effort brought together scientists representing physical sciences, chemistry, and engineering working at the nanoscale with biologists and clinicians working on cancer to form a uniquely multidisciplinary cancer nanotechnology research community. The last 14 years of the program have produced a remarkable body of scientific discovery and demonstrated its utility to the development of practical cancer interventions. This paper takes stock of how the Alliance program influenced melding of disparate research disciplines into the field of nanomedicine and cancer nanotechnology, has been highly productive in the scientific arena, and produced a mechanism of seamless transfer of novel technologies developed in academia to the clinical and commercial space. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Diagnostic Tools > in vivo Nanodiagnostics and Imaging.