SiO2/Al2O3/C grafted 3-n propylpyridinium silsesquioxane chloride-based non-enzymatic electrochemical sensor for determination of carcinogenic nitrite in food products

The excessive uptake of nitrite is perilous and detrimental for human health that prone to cancer disease. Herein, described the synthesis of SiO₂/Al₂O₃/C material through the sol-gel procedure followed by grafting with 3-n propylpyridinium silsesquioxane chloride organic ligand for enhancing electrochemical activity. H-NMR, ¹³C NMR, and ²⁹Si studies were performed for confirmation of surface functionalization through the grafting technique. The surface morphology was evaluated through SEM and TEM techniques. The material showed an irregular and flakes-like structure that exhibited more compactness and conglomerate structure with no segregation in phase was observed after grafting. The elemental composition was confirmed from EDX analysis. The electrochemical measurements were performed with cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and chronoamperometry. The prepared hybrid inorganic-organic composite Si/C/Al/SiPy⁺Cl^- was applied for the modification of the glassy carbon (GC) electrode and assessed as a sensor for nitrite determination. The sensor showed the low limit of detection (0.01 μM), low limit of quantification (0.08 μM), wide linear response range (0.2-280 μM), and high sensitivity (410 μA·μM^-1). It gave a quick response time of <1 s in the presence of 70 μM nitrite. The fabricated sensor showed high sensitivity, chemical stability, and insignificant interference from co-existing species present in sausage meat and food industry discharges. The repeatability of the sensor was evaluated as 2.5 % R.S.D.; for n = 10 at 50 μM nitrite.

Polymer dewetting in solvent-non-solvent environment- new insights on dynamics and lithography-free patterning

HYPOTHESIS

We show that one may employ polymer dewetting in solvent-non-solvent environment to obtain lithography-free fabrication of well-defined nano- to micro- scale polymer droplets arrays from pre-patterned polymer films. The polymer droplet pattern may be converted to a series of hybrid organic-inorganic and inorganic well-defined nano-patterns by using sequential infiltration synthesis (SIS). In particular, we scrutinize the physical parameters which govern the dewetting of flat and striped polymer thin films, which is the key to obtaining our objective of lithography-free ordered nano-patterns.

EXPERIMENTS

We immerse polystyrene (PS) and polymethyl methacrylate (PMMA) thin films in water in the presence of chloroform vapors. We study the ensuing polymer dewetting dynamics and the pattern formation of nanospheres by employing in-situ light microscopy and scanning electron microscopy. We then investigate pattern formation by dewetting of polymer stripes, fabricated by directed solvent evaporation, and SIS of AlO_x from vapor phase precursors, trimethyl aluminum (TMA) and H₂O, within the nanosphere patterns.

FINDINGS

We find that solvent- non-solvent environments render film dewetting rates, which are an order of magnitude faster than solvent vapor dewetting, and supports the formation of small solid polymer droplets, down to sub-100 nm droplet size, of large contact angles with the solid substrate. Pre-patterned polymer film stripes support the formation of highly ordered structures of polymer droplets, which are easily transformed to hybrid polymer-AlO_x nanosphere patterns and templated AlO_x nanosphere via SIS.