Magnetoelastic sensors for real-time tracking of cell growth.

Magnetoelastic (ME) sensors, which can be remotely activated via magnetic fields, are an excellent choice for wireless monitoring of biological parameters due to their ability to be scaled into different sizes and have their surface functionalized for chemical or biological sensing. In this study, we present the application of a commercially available ME material (Metglas 2826 MB) to develop a sensor system that can monitor the attachment of anchorage-dependent mammalian cells in two-dimensional in vitro cell cultures. Results obtained with the developed sensors and detection system correlated with microscopic image analysis of cell quantification, which showed a linear relationship between the sensor response and attached fibroblast cells on the sensor surface. It was also revealed that the developed ME sensor system is capable of providing temporal profiles of cell growth corresponding to different stages of cell attachment and proliferation in real-time.

Correlating the mass and mechanical property changes during the degradation of PEG-based adhesive.

Change in mechanical property of a degrading adhesive is critical to its performance. However, characterization of degradation behavior is often limited to tracking its mass loss. 4-armed PEG end modified with dopamine (PEG-DA) was used as a model bioadhesive to correlate its change in mass with change in mechanical property. Shear modulus (G) was calculated based on the mass and average molecular weight between crosslinks ( M ¯ c ) of PEG-DA, while the storage modulus (G') was determined by oscillatory rheometry. G decreased slowly within the first week of degradation (10% reduction by week 2), while G' decreased by 60% during the same period. This large discrepancy is due to the partially disconnected and elastically ineffective PEG polymer, which is trapped within the adhesive network. This resulted in minimal mass change and higher calculated G value during the earlier time points. Therefore, tracking mass loss profile alone is inadequate to completely describe the degradation behavior of an adhesive. Additionally, PEG-DA was coated onto magnetoelastic (ME) sensors, and the change in the resonance amplitude of the sensor corresponded well with dry mass loss of PEG-DA. ME sensing provide a non-destructive method to track the mass loss of the coated adhesive.

A rapid highly-sensitive endotoxin detection system.

This paper presents a rapid, highly-sensitive, and low-cost method of endotoxin quantification based on the use of stress-responsive magnetoelastic sensors, that monitor the gel formation (viscosity change) of the Limulus Amoebocyte Lysate (LAL) assay in response to endotoxin. Ribbon-like magnetoelastic sensors, 12.7 mm x 6 mm x 28 microm, were immersed in a LAL assay after mixing with test samples of variable endotoxin concentration, and the decrease in resonance amplitude of the sensor was recorded as a function of time. Experimental results show excellent correlation between endotoxin concentration and the maximum clot rate, determined by taking the minimum point of the first derivative of the amplitude-time curve, as well as the clotting-time, defined as the time that corresponds to the maximum clot rate. Using a LAL gel-clot assay with a sensitivity of 0.06 EU/ml (EU: endotoxin unit), the magnetoelastic sensor based technology can detect the presence of endotoxin at 0.0105 EU/ml in test requiring approximately 20 min. Unlike optical methods used for determining endotoxin concentration, the color of the test solution does not impact the magnetoelastic sensor measurement. Due to the small size of the sensor reader electronics and low cost, the magnetoelastic sensor based endotoxin detection system is ideally suited for wide-spread use in endotoxin screening for sepsis prevention.

Tracking the harmonic response of magnetically-soft sensors for wireless temperature, stress, and corrosive monitoring.

This paper describes the application of magnetically-soft ribbon-like sensors for measurement of temperature and stress, as well as corrosive monitoring, based upon changes in the amplitudes of the higher-order harmonics generated by the sensors in response to a magnetic interrogation signal. The sensors operate independently of mass loading, and so can be placed or rigidly embedded inside nonmetallic, opaque structures such as concrete or plastic. The passive harmonic-based sensor is remotely monitored through a single coplanar interrogation and detection coil. Effects due to the relative location of the sensor are eliminated by tracking harmonic amplitude ratios, thereby, enabling wide area monitoring. The wireless, passive, mass loading independent nature of the described sensor platform makes it ideally suited for long-term structural monitoring applications, such as measurement of temperature and stress inside concrete structures. A theoretical model is presented to explain the origin and behavior of the higher-order harmonics in response to temperature and stress.

A wireless magnetoelastic biosensor for the direct detection of organophosphorus pesticides.

An organophosphorus (OP) pesticide sensor was fabricated by applying a pH-sensitive polymer coating and organophosphorus hydrolase (OPH) enzyme onto the surface of a magnetoelastic sensor, the magnetic analogue of the better-known surface acoustic wave sensor. Organophosphorus hydrolase catalyses the hydrolysis of a wide range of organophosphorus compounds, which changes the pH in the hydrogel. This article describes the application of the magnetoelastic sensor for the detection of OP pesticides by measuring the changes in viscoelasticity caused by the swelling/shrinking of the pH-responsive polymer when exposed to the pesticides. The sensor was successfully used to detect paraoxon and parathion down to a concentration of 1 x 10(-7) and 8.5 x 10(-7) M respectively.