Reusable, Non-Invasive, and Ultrafast Radio Frequency Biosensor Based on Optimized Integrated Passive Device Fabrication Process for Quantitative Detection of Glucose Levels.

The increase in the number of people suffering diabetes has been the driving force behind the development of glucose sensors to overcome the current testing shortcomings. In this work, a reusable, non-invasive and ultrafast radio frequency biosensor based on optimized integrated passive device fabrication process for quantitative detection of glucose level was developed. With the aid of the novel biosensor design with hammer-shaped capacitors for carrying out detection, both the resonance frequency and magnitude of reflection coefficient can be applied to map the different glucose levels. Meanwhile, the corresponding fabrication process was developed, providing an approach for achieving quantitative detection and a structure without metal-insulator-metal type capacitor that realizes low cost and high reliability. To enhance the sensitivity of biosensor, a 3-min dry etching treatment based on chlorine/argon-based plasma was implemented for realizing hydrophilicity of capacitor surface to ensure that the biosensor can be touched rapidly with glucose. Based on above implementation, a non-invasive biosensor having an ultrafast response time of superior to 0.85 s, ultralow LOD of 8.01 mg/dL and excellent reusability verified through five sets of measurements are realized. The proposed approaches are not limited the development of a stable and accurate platform for the detection of glucose levels but also presents a scheme toward the detection of glucose levels in human serum.

Noninvasive and Continuous Monitoring of On-Chip Stem Cell Osteogenesis Using a Reusable Electrochemical Immunobiosensor.

Noninvasive monitoring of biofabricated tissues during the biomanufacturing process is needed to obtain reproducible, healthy, and functional tissues. Measuring the levels of biomarkers secreted from tissues is a promising strategy to understand the status of tissues during biofabrication. Continuous and real-time information from cultivated tissues enables users to achieve scalable manufacturing. Label-free biosensors are promising candidates for detecting cell secretomes since they can be noninvasive and do not require labor-intensive processes such as cell lysing. Moreover, most conventional monitoring techniques are single-use, conducted at the end of the fabrication process, and, challengingly, are not permissive to in-line and continual detection. To address these challenges, we developed a noninvasive and continual monitoring platform to evaluate the status of cells during the biofabrication process, with a particular focus on monitoring the transient processes that stem cells go through during in vitro differentiation over extended periods. We designed and evaluated a reusable electrochemical immunosensor with the capacity for detecting trace amounts of secreted osteogenic markers, such as osteopontin (OPN). The sensor has a low limit of detection (LOD), high sensitivity, and outstanding selectivity in complex biological media. We used this OPN immunosensor to continuously monitor on-chip osteogenesis of human mesenchymal stem cells (hMSCs) cultured 2D and 3D hydrogel constructs inside a microfluidic bioreactor for more than a month and were able to observe changing levels of OPN secretion during culture. The proposed platform can potentially be adopted for monitoring a variety of biological applications and further developed into a fully automated system for applications in advanced cellular biomanufacturing.

Black Phosphorus-Based Reusable Biosensor Platforms for the Ultrasensitive Detection of Cortisol in Saliva.

A black phosphorus (BP)-based reusable biosensor platform is developed for the repeated and real-time detection of cortisol using antibody-conjugated magnetic particle (MP) structures as a refreshable receptor. Here, we took advantage of the low-noise characteristics of a mechanically exfoliated BP-based field-effect transistor (FET) and hybridized it with anti-cortisol antibody-functionalized MPs to build a highly sensitive cortisol sensor. This strategy allowed us to detect cortisol down to 1 aM in real time and discriminate cortisol from other hormones. In this case, we could easily remove MPs with used antibodies from the surface of a BP-FET and reuse the chip for up to eight repeated sensing operations. Moreover, since our platform could be fabricated using conventional photolithography techniques and the sensor can be reused multiple times, one should be able to significantly reduce operation costs for practical applications. Furthermore, this method could be utilized to detect different hormones with high sensitivity and selectivity in complex environments such as artificial saliva solutions. In this respect, our reusable BP-FET biosensing platform can be a powerful tool for versatile applications such as clinical diagnosis and basic biological analysis by conjugating various antibodies.

Automated System for Attomolar-Level Detection of MiRNA as a Biomarker for Influenza A Virus.

We have developed an automated sensing system for the repeated detection of a specific microRNA (miRNA) of the influenza A (H1N1) virus. In this work, magnetic particles functionalized with DNAs, target miRNAs, and alkaline phosphate (ALP) enzymes formed sandwich structures. These particles were trapped on nickel (Ni) patterns of our sensor chip by an external magnetic field. Then, additional electrical signals from electrochemical markers generated by ALP enzymes were measured using the sensor, enabling the highly sensitive detection of target miRNA. The magnetic particles used on the sensor were easily removed by applying the opposite direction of external magnetic fields, which allowed us to repeat sensing measurements. As a proof of concept, we demonstrated the detection of miRNA-1254, one of the biomarkers for the H1N1 virus, with a high sensitivity down to 1 aM in real time. Moreover, our sensor could selectively detect the target from other miRNA samples. Importantly, our sensor chip showed reliable electrical signals even after six repeated miRNA sensing measurements. Furthermore, we achieved technical advances to utilize our sensor platform as part of an automated sensing system. In this regard, our reusable sensing platform could be utilized for versatile applications in the field of miRNA detection and basic research.

Environmental electroactive consortia as reusable biosensing element for freshwater toxicity monitoring.

The development of tools to monitor water quality is mandatory in a scenario where clean water resources are decreasing. Here, the biosensing capability of an electroactive river sediment consortium was tested towards three model contaminants (glutaraldehyde, nickel(II) and chromium(III)). The proposed biosensor is a small membrane-less single chamber Microbial Fuel Cell (MFC), fabricated by 3D printing. Its semi-continuous mode of operation resulted in long-term current profile stability and reproducibility. A linear trend of response was obtained for glutaraldehyde in a concentration range of 5-1000 ppm. After the recovery of the electroactive consortium activity, the MFC-based biosensors were shown to be sensitive towards Ni(II) and Cr(III), at concentrations above 2 mg L-1. To effectively analyze biosensor response, a novel algorithm was proposed, offering advantages for the realization of energy-saving protocols for MFC-biosensor data transmission. Implementation of the device and method, from laboratory test to real environment, can offer a low cost in situ system for detection of water contaminants.

Isoelectric Bovine Serum Albumin: Robust Blocking Agent for Enhanced Performance in Optical-Fiber Based DNA Sensing.

Surface blocking is a well-known process for reducing unwanted nonspecific adsorption in sensor fabrication, especially important in the emerging field where DNA/RNA applied. Bovine serum albumin (BSA) is one of the most popular blocking agents with an isoelectric point at pH 4.6. Although it is widely recognized that the adsorption of a blocking agent is strongly affected by its net charge and the maximum adsorption is often observed under its isoelectric form, BSA has long been perfunctorily used for blocking merely in neutral solution, showing poor blocking performances in the optical-fiber evanescent wave (OFEW) based sensing toward DNA target. To meet this challenge, we first put forward the view that isoelectric BSA (iep-BSA) has the best blocking performance and use an OFEW sensor platform to demonstrate this concept. An optical-fiber was covalently modified with amino-DNA, and further coupled with the optical system to detect fluorophore labeled complementary DNA within the evanescent field. A dramatic improvement in the reusability of this DNA modified sensing surface was achieved with 120 stable detection cycles, which ensured accurate quantitative bioassay. As expected, the iep-BSA blocked OFEW system showed enhanced sensing performance toward target DNA with a detection limit of 125 pM. To the best of our knowledge, this is the highest number of regeneration cycles ever reported for a DNA immobilized optical-fiber surface. This study can also serve as a good reference and provide important implications for developing similar DNA-directed surface biosensors.

A reusable robust radio frequency biosensor using microwave resonator by integrated passive device technology for quantitative detection of glucose level.

A reusable robust radio frequency (RF) biosensor with a rectangular meandered line (RML) resonator on a gallium arsenide substrate by integrated passive device (IPD) technology was designed, fabricated and tested to enable the real-time identification of the glucose level in human serum. The air-bridge structure fabricated by an IPD technology was applied to the RML resonator to improve its sensitivity by increasing the magnitude of the return loss (S21). The resonance behaviour, based on S21 characteristics of the biosensor, was analysed at 9.20 GHz with human serum containing different glucose concentration ranging from 148-268 mg dl(-1), 105-225 mg dl(-1) and at a deionised (D) water glucose concentration in the range of 25- 500 mg dl(-1) for seven different samples. A calibration analysis was performed for the human serum from two different subjects and for D-glucose at a response time of 60 s; the reproducibility, the minimum shift in resonance frequency and the long-term stability of the signal were investigated. The feature characteristics based on the resonance concept after the use of serum as an analyte are modelled as an inductor, capacitor and resistor. The findings support the development of resonance-based sensing with an excellent sensitivity of 1.08 MHz per 1 mg dl(-1), a detection limit of 8.01 mg dl(-1), and a limit of quantisation of 24.30 mg dl(-1).

A reusable optical biosensor for the ultrasensitive and selective detection of unamplified human genomic DNA with gold nanostars.

A Surface Plasmon Resonance imaging (SPRi) based DNA sensors for the selective and ultrasensitive human genomic DNA detection, directly extracted from lymphocytes (bypassing PCR amplification), is reported. To achieve DNA detection, a rationally chosen star-shaped nanoparticle (NP), namely gold nanostar (AuNS), has been applied, for the first time, in a sandwich-like assay based on the selective capturing of specific DNA targets and the subsequent signal amplification by a secondary DNA probe linked to AuNS. The plasmonic profile, size and electric field enhancements at the star tips contributed to the maximization of plasmon coupling between LSPs and SPs as aimed for analytical signal magnification. The system was first tested using short synthetic DNA target sequences and applied to DNA biosensing, lowering 610-fold the detection limit from 6.1 nM (without NSs labeling) to 10 pM (with NSs labeling). Then the biosensor was applied to genomic DNA samples, extracted from human lymphocytes and undergoing only to a simple ultrasonic fragmentation, lowering (~435 fold) the detection limit from 3.0 fM (without NSs labeling) to 6.9 aM (with NSs labeling). Thanks to the assay optimization, we proved that tuning the NSs surface coverage with DNA linked to nanoparticles is crucial not only for the increase of signals but also for the regenerability/reusability of the biosensor for tens of measurement cycles.

A reusable magnetic graphene oxide-modified biosensor for vascular endothelial growth factor detection in cancer diagnosis.

Early cancer diagnosis is critical for the prevention of metastasis. However, simple and efficient methods are needed to improve the diagnosis and evaluation of cancer. Here, we propose a reusable biosensor based on a magnetic graphene oxide (MGO)-modified Au electrode to detect vascular endothelial growth factor (VEGF) in human plasma for cancer diagnosis. In this biosensor, Avastin is used as the specific biorecognition element, and MGO is used as the carrier for Avastin loading. The use of MGO enables rapid purification due to its magnetic properties, which prevents the loss of bioactivity. Moreover, the biosensor can be constructed quickly, without requiring a drying process, which is convenient for proceeding to detection. Our reusable biosensor provides the appropriate sensitivity for clinical diagnostics and has a wide range of linear detection, from 31.25-2000 pg mL(-1), compared to ELISA analysis. In addition, in experiments with 100% serum from clinical samples, readouts from the sensor and an ELISA for VEGF showed good correlation within the limits of the ELISA kit. The relative standard deviation (RSD) of the change in current (ΔC) for reproducibility of the Au biosensor was 2.36% (n=50), indicating that it can be reused with high reproducibility. Furthermore, the advantages of the Avastin-MGO-modified biosensor for VEGF detection are that it provides an efficient detection strategy that not only improves the detection ability but also reduces the cost and decreases the response time by 10-fold, indicating its potential as a diagnosis product.