A simple and sensitive colorimetric gold nanoparticle probe for detection of melamine in infant formula was developed by the reduction of Au(III) salt with sodium citrate. This method is rather simple that does not involve any surface modification of the nanoparticles or multistep sample treatment. This technique is based on the fact that the optical properties of gold nanoparticles depend on distance between particles. Gold nanoparticles are aggregated in a neutral media in the presence of melamine; this causes an easily measurable change in the absorption spectrum of the particles, which can be monitored with the naked eye or UV-vis spectrophotometer. Here, the color of gold nanoparticles changed from wine red to blue in the presence of melamine and no color change was observed before melamine was introduced into the milk sample. The observed color change is the result of the coupling of the surface plasmon resonance (SPR) between particles in close proximity. This method is also sensitive and a limit of detection of 0.90 ppm of melamine was obtained with the UV-vis spectrophotometer in aqueous solution and 0.46 ppm of melamine was detected visually with the naked eye in a solution of infant formula.

Experiments in laboratory manuals intended for general, organic, and biological (GOB) chemistry laboratories include few opportunities for students to engage in instrumental methods of analysis. Many of these students seek careers in modern health-related fields where experience in spectroscopic techniques would be beneficial. A simple, rapid, easily implemented experiment was developed to measure vitamin C levels in solutions using visible spectroscopy. When vitamin C is added to a mixed reagent containing Fe 3+ and 1,10-phenanthroline, the vitamin C reduces the Fe 3+ to Fe 2+ which subsequently combines with the 1,10-phenanthroline to form a reddish-orange colored complex that is measured by visible spectroscopy at 510 nm. The experiment includes measurement of the stability of aqueous vitamin C solutions when exposed to long-term storage and to heat. Students in GOB laboratory classes were able to produce results with good precision. The experiment was also extended to include the measurement of vitamin C in nutrition supplements.

Phosphorylcholine (PC) based phospholipid bilayers have proven useful as capillary coating materials due to their inherent resistance to non-specific protein adsorption. The primary limitation of this important class of capillary coatings remains the limited long-term chemical and physical stability of the coatings. Recently, a method for increasing phospholipid coating stability in fused silica capillaries via utilization of polymerized, synthetic phospholipids was reported. Here, we expand upon these studies by investigating polymerized lipid bilayer capillary coatings with respect to separation performance including run-to-run, day-to-day and column-to-column reproducibility and long term stability. In addition, the effects of pH and capillary inner diameter on polymerized phospholipid coated capillaries were investigated to identify optimized coating conditions. The coatings are stabilized for protein separations across a wide range of pH values (4.0-9.3), a unique property for capillary coating materials. Additionally, smaller inner diameter capillaries (≤ 50 μm) were found to yield marked enhancements in coating stability and reproducibility compared to wider bore capillaries, demonstrating the importance of capillary size for separations employing polymerized phospholipid coatings.

Protein separations in capillary zone electrophoresis (CZE) suffer from non-specific adsorption of analytes to the capillary surface. Semi-permanent phospholipid bilayers (PLBs) have been used to minimize adsorption, but must be regenerated regularly to ensure reproducibility. We investigated the formation, characterization, and use of hybrid phospholipid bilayers (HPBs) as more stable biosurfactant capillary coatings for CZE protein separations. HPBs are formed by covalently modifying a support with a hydrophobic monolayer onto which a self-assembled lipid monolayer is deposited. Monolayers prepared in capillaries using 3-cyanopropyldimethylchlorosilane (CPDCS) or n-octyldimethylchlorosilane (ODCS) yielded hydrophobic surfaces with lowered surface free energies of 6.0 ± 0.3 or 0.2 ± 0.1 mJ m−2, respectively, compared to 17 ± 1 mJ m−2 for bare silica capillaries. HPBs were formed by subsequently fusing vesicles comprised of 1,2-dilauroyl-sn-glycero-3-phosphocholine or 1,2-dioleoyl-sn-glycero-3-phosphocholine to CPDCS- or ODCS-modified capillaries. The resultant HPB coatings shielded the capillary surface and yielded reduced electroosmotic mobility (1.3 – 1.9 × 10−4 cm2 V−1s−1) compared to CPDCS- and ODCS-modified or bare capillaries (3.6 ± 0.2 × 10−4 cm2 V−1s−1, 4.8 ± 0.4 × 10−4 cm2 V−1s−1, and 6.0 ± 0.2 × 10−4 cm2 V−1s−1, respectively), with increased stability compared to PLB coatings. HPB-coated capillaries yielded reproducible protein migration times (RSD ≤ 3.6 %, n ≥ 6) with separation efficiencies as high as 200,000 plates m−1.