Dynamic behaviour of the silica-water-bio electrical double layer in the presence of a divalent electrolyte.

Electronic devices are becoming increasingly used in chemical- and bio-sensing applications and therefore understanding the silica-electrolyte interface at the atomic scale is becoming increasingly important. For example, field-effect biosensors (BioFETs) operate by measuring perturbations in the electric field produced by the electrical double layer due to biomolecules binding on the surface. In this paper, explicit-solvent atomistic calculations of this electric field are presented and the structure and dynamics of the interface are investigated in different ionic strengths using molecular dynamics simulations. Novel results from simulation of the addition of DNA molecules and divalent ions are also presented, the latter of particular importance in both physiological solutions and biosensing experiments. The simulations demonstrated evidence of charge inversion, which is known to occur experimentally for divalent electrolyte systems. A strong interaction between ions and DNA phosphate groups was demonstrated in mixed electrolyte solutions, which are relevant to experimental observations of device sensitivity in the literature. The bound DNA resulted in local changes to the electric field at the surface; however, the spatial- and temporal-mean electric field showed no significant change. This result is explained by strong screening resulting from a combination of strongly polarised water and a compact layer of counterions around the DNA and silica surface. This work suggests that the saturation of the Stern layer is an important factor in determining BioFET response to increased salt concentration and provides novel insight into the interplay between ions and the EDL.

Molecular dynamics simulation of potentiometric sensor response: the effect of biomolecules, surface morphology and surface charge.

The silica-water interface is critical to many modern technologies in chemical engineering and biosensing. One technology used commonly in biosensors, the potentiometric sensor, operates by measuring the changes in electric potential due to changes in the interfacial electric field. Predictive modelling of this response caused by surface binding of biomolecules remains highly challenging. In this work, through the most extensive molecular dynamics simulation of the silica-water interfacial potential and electric field to date, we report a novel prediction and explanation of the effects of nano-morphology on sensor response. Amorphous silica demonstrated a larger potentiometric response than an equivalent crystalline silica model due to increased sodium adsorption, in agreement with experiments showing improved sensor response with nano-texturing. We provide proof-of-concept that molecular dynamics can be used as a complementary tool for potentiometric biosensor response prediction. Effects that are conventionally neglected, such as surface morphology, water polarisation, biomolecule dynamics and finite-size effects, are explicitly modelled.

Are general practitioners really prepared? An audit of emergency equipment in general practice.

AIM: To determine what medical equipment is available in general practice surgeries in the greater Wellington region and the guidelines available for providing this equipment. METHOD: A 23 item questionnaire was completed by general practices in the greater Wellington region between March and June 1993. RESULTS: Sixty-three percent of the study practices did not have all the required items the authors considered essential. CONCLUSION: There is a clear need for guidelines on required emergency equipment for those working in or wishing to set up in general practice.

Effect of nursing reassurance on patient vocal stress levels.

To compare effect of two types of nursing reassurances on patient anxiety or stress, as measured vocally by the Psychological Stress Evaluator, 23 subjects with confirmed pregnancies were interviewed by two registered nurses regarding their concerns about hospitalization. Each subject served as her own control. Vocal stress was measured from audiotapes of the nurse-subject interactions. Fourteen subjects; received "knowledgeable" (R2) reassurance; nine received "superficial" (R1) reassurance. Both types of nursing reassurances seemed to be effective with regard to vocal stress patterns. Three subjects who received knowledgeable reassurance showed decreased vocal stress: no subjects who received superficialreassurance showed decrease. There were no significant differences in the interaction length among the three groups of vocal stress patterns of subjects who received knowledgeable reassurance or between the two groups who received superficial reassurance. The data suggested that differences in vocal stress did not result from more or less talking by the subjects. Distribution of vocal stress changes observed in both types of reassurance led to investigation of the patient variable of denial as a possible explanation for the reason why knowledgeable reassurance was associated with increases in vocal stress for some subjects. The results that knowledgeable reassurance may be more beneficial regarding the reduction of stress than superficial reassurance, but only for subjects who do not utilize denial or avoidance as a coping mechanism. The study indicated that, for the majority, one of the benefits of academically promulgated knowledgeable reassurance is probably not the immediate reduction of subject anxiety or stress.