RESUMO
Paper is a versatile, flexible, porous, and eco-friendly substrate that is utilized in the fabrication of low-cost devices and biosensors for rapid detection of analytes of interest. Paper-based sensors provide affordable platforms for simple, accurate, and rapid detection of diseases, in addition to monitoring food quality, environmental and sun exposure, and detection of pathogens. Paper-based devices provide an inexpensive technology for fabrication of simple and portable diagnostic systems that can be immensely useful in resource-limited settings, such as in developing countries or austere environments, where fully-equipped facilities and highly trained medical staff are absent. In this work, we present the different types of paper that are currently utilized in fabrication of paper-based sensors, and common fabrication techniques ranging from wax printing to origami- and kirigami-based approaches. In addition, we present different detection techniques that are employed in paper-based sensors such as colorimetric, electrochemical, and fluorescence detection, chemiluminescence, and electrochemiluminescence, as well as their applications including disease diagnostics, cell cultures, monitoring sun exposure, and analysis of environmental reagents including pollutants. Furthermore, main advantages and disadvantages of different types of paper and future trends for paper-based sensors are discussed.
RESUMO
Purpose: This report describes the technique of utilizing a neutral density filter (NDF) during Scheimpflug imaging of a dense corneal opacity in order to increase data acquisition success and improve data reliability for densitometry analysis. Observations: A 49-year-old female with Steven-Johnson Syndrome secondary to sulfonamide use presented for routine follow up evaluation of her customized ocular surface prosthetic device (PD). Her ocular history was significant for mucous membrane grafting and limbal stem cell transplant in both eyes. The ocular surface examination of the left eye was notable for chronic dense neovascularization and scarring of the temporal and inferior cornea which extended into the visual axis. Scheimpflug imaging and densitometry analysis were performed in order to quantify the severity of the scar, however, there was significant difficulty in acquiring densitometry data. During a subsequent follow-up visit to monitor the scar, standardized room lighting and a neutral density filter were used to obtain reproducible and reliable imaging for densitometry analysis. The corneal scar was monitored over time using this standardized imaging protocol and by densitometry analysis minimal progression of the scar was evident, suggesting that recently documented significant vision loss in the left eye could not be attributed solely to changes in the scar. Conclusion and Importance: The use of a neutral density filter along with standardized ambient lighting conditions when performing Scheimpflug imaging may be necessary to reliably monitor densitometry progression of clinically severe corneal opacities.