Time-gated techniques are useful for the rapid sampling of excited-state (fluorescence) emission decays in the time domain. Gated detectors coupled with bright, economical, nanosecond-pulsed light sources like flashlamps and nitrogen lasers are an attractive combination for bioanalytical and biomedical applications. Here we present a calibration approach for lifetime determination that is noniterative and that does not assume a negligible instrument response function (i.e., a negligible excitation pulse width) as does most current rapid lifetime determination approaches. Analogous to a transducer-based sensor, signals from fluorophores of known lifetime (0.5-12 ns) serve as calibration references. A fast avalanche photodiode and a GHz-bandwidth digital oscilloscope is used to detect transient emission from reference samples excited using a nitrogen laser. We find that the normalized time-integrated emission signal is proportional to the lifetime, which can be determined with good reproducibility (typically <100 ps) even for data with poor signal-to-noise ratios ( approximately 20). Results are in good agreement with simulations. Additionally, a new time-gating scheme for fluorescence lifetime imaging applications is proposed. In conclusion, a calibration-based approach is a valuable analysis tool for the rapid determination of lifetime in applications using time-gated detection and finite pulse width excitation.

Currently, the available technologies that are capable of monitoring pulse wave velocity (PWV) in a patient are uncomfortable and obstructive. Recently, it has been hypothesized the use of photoplethysmographic (PPG) for this purpose and, therefore, the need to capture and understand the hemodynamic variables used in the PPG signal acquirement process, such as the local pulse transit time (PTT) and local PWV. This work aims to verify the feasibility of the PPG technique in the construction of local PTT and PWV monitor, using PPG sensors and low-cost integrated circuits. In this paper, the low-cost term is used as a synonym for retail sensors, available commercially and commonly used in academic projects for the Arduino platform. It is important for the development of wearable technologies that can be used in a future project to monitor PTT and PWV using a minimally obstructive approach.