Bio-Terge AS-40. tm

We used this surfactant effectively in solving some wetting and solubility problems during the development of a dry-phase urinary test device. We were experiencing a mottled color response and somewhat slow reaction times. We had a water-insoluble indicator that had resolubilize in an aqueous biological fluid, knew that wetting and solubility were the chief problem areas. We also knew that our current surfactnt, being applied in a pH 9 aqueous system, was helping somewhat, and thus launched a screen over a  dozen likely surfactant choices. Bio-Terge AS-40,a mild anionic surfactant, stood out head-and-shoulders above the other candidates. The color response was strikingly better in appearance, with significant reaction speed gains.

Ninate 411. tm

In another impregnation mix, we were using methylisobutylketone (MIBK) as impregnation solvent. This was a highly desirable choice over acetone for both safety and reagent stability (MIBK does not absorb water) reasons. Unfortunately, the diazonium salt we were using precipitated out of solution during the impregnation run and could not be substituted by another. We had been using no surfactant at all, and in fact rarely if ever did in organic solvents. A screen for MIBK soluble surfactants produced 6 or 8 candidates, which we then tested to hold the diazonium salt in solution. Ninate 411 was the clear winner, and now afforded us unlimited pot-life times with regard to diazonium salt stability.

Aerosol OT 100%. tm

This surfactant is essential for tetramethylbenzidine (TMB) stability. TMB is an oxidative-type indicator that readily overoxi-izes to a cruddy brown color that is undesirable for either visual or instrumental readout. Aerosol OT stops the oxidation process at the nice classic robins-egg blue color. Aerosol OT is believed to accomplish this through a complexing with the TMB. The complex is tightest at the first oxidation state of TMB, and is thus stabilized at that point. Aerosol OT/TMB systems are soluble in organic solvents such as toluene. It can also be used in aqueous solutions, in which case TMB-HCI would be the appropriate indicator form.

Sodium cholate/deoxycholate.

These are important surfactants for cholesterol chemistries. Cholates are effective cholesterol solubilizers and cholesterol enzyme activators due to the common steroidal-like backbone structure of these surfactants and cholesterol. It is a good idea to try more than one cholate in a screen, since solubility characteristics can vary with factors such as pH and ionic strength.


SILWET L7600. tm

This is a unique siloxane-based surfactant with excellent wetting power. SILWET L7600 is among the few surfactants capable of wetting Teflon (PTFE) surfaces. It is highly soluble in both water and many organic solvents. We found this surfactant particularly useful once in a the development of a solid-phase whole-blood diagnostic device that was yielding biased numbers at high RBC hematocrit. A large array of surfactants was tested, and this was the only one that could eliminate the bias. It was thought that this surfactant through its powerful action at interfaces was interference by RBCs at the RBC-test surface interface. This surfactant is totally non-hemolytic. Typical use level is from 0.01 to 1%.

Surfynot 465/485. tm

This pair of surfactants is also very gentle on red blood cells and can be placed directly in materials used to adsorb or filter RBCs. Both surfactants improve the stability of latex suspensions when used either as sole emulsifying agent or in conjunction with other emulsifying surfactants. They are low-foaming, high-wetting,and are the surfactants of choice for achieving an even coating of membranes with reagents.Surfybnot 485 has a higher HLB and is thus somewhat more water soluble, although both are soluble in water to levels greater than 1.0%. Surfynol 465 has slightly lower surface tension.