A new gated form of phase fluorometry for measuring lifetimes is presented. The technique uses a square-wave excitation and gates the detector on only during the off period of the excitation. Using a long-lived sample, this eliminates or reduces errors from scattered light and short-lived fluorescences. Using a square-wave modulated excitation source with a 50% duty cycle, traditional data treatment can be used after, at most, a simple pi/2 phase adjustment. A combination of theory and experimental results demonstrates the validity of this new gated method and its utility for eliminating or reducing background. The results are precise, accurate, eliminate scattering errors, and greatly reduce errors due to short-lived fluorescence impurities. Errors from fluorescence bleed-through into the detection period or a slow excitation source turn off can be mitigated by using an offset time prior to gating the detector on.

Along with the advent of the human immunodeficiency virus (HIV) came a worldwide resurgence of syphilis. The later stages of syphilis, especially neurosyphilis, may present with symptoms of virtually any psychiatric disorder. The authors present three cases of neurosyphilis diagnosed at the Center for Psychiatric Medicine of the University of Alabama at Birmingham, where the patients presented with overwhelmingly psychiatric manifestations. The authors recommend that clinicians have a high index of suspicion of neurosyphilis, which may have an exclusively psychiatric presentation.

Oxygen and copper(II) ion quenching studies were conducted on a model sensor system to elucidate the significant, yet not fully characterized, role of polymer supports in sensor performance. The system consisted of [Ru(Ph2phen)2(4-cyclamCH2(4′-Me)bpy)]Cl2 (Ph2phen = 4,7-diphenyl-1,10-phenanthroline; bpy = 2,2′-bipyridine; cyclam = 1,4,8,11-tetraazacyclotetradecane) as the sensor molecule, copper(II) ions as the quenching analyte, and two polymer supports. One polymer used was a cyclic siloxane cross-linked with a hydrophilic poly(ethylene oxide); the other was a ternary polymer with poly(ethylene oxide), poly(dimethylsiloxane), and 2-hydroxyethylmethacrylate. Both polymers contain a hydrophobic binding region for the sensor molecule and a hydrated hydrophilic region for transport of the ions to the sensor. Luminescence intensity and lifetime measurements show the polymer supports to be equally effective at shielding the sensor molecule from oxygen quenching but not copper(II) ion quenching. Unlike oxygen, the copper(II) ions quench the sensor molecule in solution and in the polymer supports through a combination of static and dynamic quenching. The unquenched excited state lifetimes, bimolecular rate constants, and equilibrium constants are presented, and their differences are interpreted to provide information about the local environment of the sensor molecule immobilized in the polymer supports.