Complex biological fluids without pretreatment, separation, or purification impose stringent limitations on the practical deployment of label-free plasmonic biosensors for advanced assays needed in point of care applications. In this work, we present an enzyme-free plasmonic neurotransmitter dopamine biosensor integrated with a microfluidic plasma separator. This integrated device allows the in-line separation of plasma directly from the bloodstream and channels it to the active detection area, where inorganic cerium oxide nanoparticles function as local selective dopamine binding sites through strong surface redox reaction. A thorough understanding and engineering of the nanoparticles is carried out to maximize its dopamine sensitivity and selectivity. We obtain detection of dopamine at 100 fM concentration in simulated body fluid and 1 nM directly from blood without any prior sample preparation. The detection selectivity is found to be at least five-times higher compared to the common interfering species. This demonstration shows the feasibility of the practical implementation of the proposed plasmonic system in detection of variety of biomarkers directly from the complex biological fluids.
Cerium oxide nanoparticles (CNPs) exhibit superoxide dismutase (SOD) and catalase mimetic activities. Therefore, based on its catalytic activities, CNPs can potentially be used to treat diseases associated with oxidative stress. The potency of CNPs can be hindered by ion interaction due to chemical modifications. The issue is that phosphate ions are relatively ubiquitous in all biological relevance medium and body fluid. Our ventures in this study were to understand the phosphate ion interaction and fabricate CNPs that are biocompatible and simultaneously retain their catalytic properties in the presence of phosphate ions. CNPs were coated with polyethylene glycol and dextran in order to enhance biocompatibility. A series of experiments determined that maximizing the preserved catalytic responses were highly dependent on the Ce3+:Ce4+. Results have shown that the particles engineered with higher concentrations of Ce4+ on the surface are more robust and retain catalytic activity post buffer exposure.
Nanoporous gold (NPG) has remarkable catalytic activity and biocompatibility and could potentially be used in biomedical devices. Herein, we have assessed the long term effects of biofouling on NPG interface. Nanoporoes (25 nm) in gold electrode are fabricated using a de-alloying treatment resulting in an 18 fold increase in surface area as compared to the planar gold. The effects of biofouling on the planar gold interface were evidenced by the rapid decrease in faradaic current to 55% in just eight minutes of incubation in 2 mg ml À1 of bovine serum albumin (BSA). On the other hand NPG showed barely any decline in the peak current when incubated in a similar biofouling solution. NPG upon incubation in a solution of higher concentration of BSA showed immediate peak current degradation which was subsequently recovered when the electrode was left idle in the biofouling solution. For instance, the peak current regenerated from (60% to 80%) when left idle for 60 minutes in 16 mg ml À1 of BSA solution. The regeneration mechanism indicated that even after long term incubation in the biofouling solution, the accumulated organic layer on its interface is not impervious and allows the diffusion of small analytes molecules. Thereby, NPG could be used in biomedical devices such as biosensor or drug reservoir.
The authors investigated the role of different size and morphology of cerium oxide nanoparticles (CNPs) in cellular uptake and internalization at the nano-bio interface. Atomic force microscopy (AFM) has been utilized to record changes in the membrane elasticity as a function of ceria particle morphology and concentration. Young's Modulus was estimated in presence and absence of CNPs of different sizes by gauging the membrane elasticity of CCL30 (squamous cell carcinoma) cells. Significant change in Young's Modulus was observed for CNP treatments at higher concentrations, while minimum membrane disruption was observed at lower concentrations. Studies using blocking agents specific to energy-dependent cellular internalization pathways indicated passive cellular uptake for smaller CNPs (3-5 nm). Other observations showed that larger CNPs were unable to permeate the cell membrane, which indicates an active uptake mechanism by the cell membrane. The ability of smaller CNPs (3-5 nm) to permeate the cell membrane without energy consumption by uptake pathways suggests potential for use as nanovectors for the delivery of bioactive molecules. Specifically, the passive uptake mechanism allows for the delivery of surface-bound molecules directly to the cytoplasm, avoiding the extreme chemical conditions of endosomal pathways.
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