NAGase sensing in 3% milk: FET-based specific and label-free sensing in ultra-small samples of high ionic strength and high concentration of non-specific proteins.

Biosensing with biological field-effect transistors (bioFETs) is a promising technology toward specific, label-free, and multiplexed sensing in ultra-small samples. The current study employs the field-effect meta-nano-channel biosensor (MNC biosensor) for the detection of the enzyme N-acetyl-beta-D-glucosaminidase (NAGase), a biomarker for milk cow infections. The measurements are performed in a 0.5 µL drops of 3% commercial milk spiked with NAGase concentrations in the range of 30.3 aM-3.03 µM (Note that there is no background NAGase concentration in commercial milk). Specific and label-free sensing of NAGase is demonstrated with a limit-of-detection of 30.3 aM, a dynamic range of 11 orders of magnitude and with excellent linearity and sensitivity. Additional two important research outcomes are reported. First, the ionic strength of the examined milk is ∼120 mM which implies a bulk Debye screening length <1 nm. Conventionally, a 1 nm Debye length excludes the possibility of sensing with a recognition layer composed of surface bound anti-NAGase antibodies with a size of ∼10 nm. This apparent contradiction is removed considering the ample literature reporting antibody adsorption in a predominantly surface tilted configuration (side-on, flat-on, etc.). Secondly, milk contains a non-specific background protein concentration of 33 mg/ml, in addition to considerable amounts of micron-size heterogeneous fat structures. The reported sensing was performed without the customarily exercised surface blocking and without washing of the non-specific signal. This suggests that the role of non-specific adsorption to the BioFET sensing signal needs to be further evaluated. Control measurements are reported.

Immobilization of ssDNA on a metal-organic framework derived magnetic porous carbon (MPC) composite as a fluorescent sensing platform for the detection of arsenate ions.

In this work, we fabricated a metal-organic framework derived magnetic porous carbon (MPC) composite using a one-pot solid state template method. The formation of the synthesized composite was confirmed with various spectroscopic techniques, and it was proved that the composite can effectively quench the fluorescence of ssDNA. This property was utilized in the specific and efficient recognition of harmful arsenate ions. FAM-labelled single strand DNA (FAM-ssDNA) was adsorbed on the surface of the MPC composite and immobilized viaπ-π stacking interactions, which resulted in the fluorescence emission being quenched. A fluorescence quenching efficiency of 96% was achieved, due to the huge surface area of the MPC composite. Upon the addition of As(v) ions into our sensing system, the fluorescence emission dramatically increased, due to the strong affinity for As(v) of the surface of the MPC composite. Consequently, the adsorbed FAM-ssDNA was spontaneously displaced from the surface of the MPC composite, and so the fluorescence intensity was regained. Based on this mechanism, the fabricated biosensor exhibited a highly sensitive fluorescence response to As(v) in the range from 0 to 15 nM, with a detection limit as low as 630 pM. Furthermore, the sensing system is suitable for diverse biological and environmental samples.