Prototyping a Microfluidic Sensor for Real-Time Detection of Airborne Formaldehyde

Abstract

Formaldehyde is a carcinogenic volatile organic compound that is largely used in the fabrication process of a variety of household products, being sometimes released indoor in concentrations that are beyond the limits recommended by the World Health Organization. The current commercially available formaldehyde sensors are far from simultaneously being ultra-portable, highly sensitive (< 1 ppb), real-time, and especially cost-efficient. This work aims to study the feasibility to miniaturize the formaldehyde sensing system down to a palm hand device, based on the microfluidic Hantzsch reaction method and fluorescence detection. A Gas-Liquid Micro-Reactor based on integration of a hydrophobic membrane inside a polymer flat chip is proposed and its formaldehyde trapping yield is planned to be further tested. By combining contact sensing with time-resolved CMOS sensors, the dimensions of the fluorescence detection component could go down to 10 mm × 20 mm × 30 mm by using commercialavailable components and therefore, enabling continuous and fast-response measurements using small volumes and low concentration samples. Index Terms-Contact sensing, micro-fabrication, on-chip membrane-based gas-liquid contacting, time-resolved CMOS sensing.

Optofluidic Formaldehyde Sensing: Towards On-Chip Integration

“…This would further diminish the optical path length and lead towards a fully-integrated monolithic device. Moreover, a filterless configuration based on time-resolved detection methodology could be employed, as described by Mariuta et al [ 16 ]. This methodology practically avoids the optical background noise, but its implementation is strictly related to the working frequency of the processor involved, since the DDL molecule fluorescence decay time is only limited to 2 ns.…”

“…Regarding the challenge related to airborne HCHO trapping in a microfluidic context, a gas–liquid microreactor concept was proposed [ 16 ]. A disposable gas–liquid microcontactor, designed as a two-layer PMMA structure with an embedded polymeric membrane, is supposed to be integrated in between two holders equipped with an integrated heating and fluidic streaming system.…”

“…During step (2), the HCHO molecules from the air are trapped in a 4-amino-3-penten-2-one (Fluoral-P) or acetylacetone solution. The molecular transfer from the gaseous phase to the liquid phase is characterized by a convection–diffusion mechanism [ 16 ]. The efficiency of the diffusion process is strictly related to a couple of parameters, such as the contacting area between the two phases, the contacting time, and the molecular driving forces across the gas–liquid interface (e.g., partial pressure difference, chemical potential, concentration difference) [ 17 ].…”

“…This challenge was split into two individually addressed problems: (1) efficient airborne HCHO trapping in a microfluidic context and (2) low-concentration DDL molecular sensing in reduced interrogation volumes. Problem (1) was partially addressed and a gas–liquid microreactor concept was built around a disposable membrane-based PMMA flat contactor [ 16 ]. Problem (2) was addressed by proposing, fabricating, and testing a fluorescence detection system based on an ultrasensitive CMOS image sensor.…”

Miniaturization of fluorescence sensing in optofluidic devices

“…Downscaling chemical and biological sensors result not only in ultra-portable devices, but in advantages such as enhanced process performance, higher analysis speed and reduced reagent consumption, significantly lowering fabrication, maintenance, and operational costs (Shakoor et al 2018). Some fields that benefit from these achievements are healthcare monitoring (Boppart and Richards-Kortum 2014; Wessels and Raad 2016;Zi et al 2016;Papageorgiou et al 2017;Sharma et al 2018), organ-on-a-chip (Zhang et al 2015;Si Hadj Mohand et al 2017;Kilic et al 2018), drug screening (Zhang et al 2015), food monitoring (Bhattacharya et al 2017), and environment monitoring (Ricciardi et al 2015a;Calvé et al 2017;Rezende et al 2019;Măriuța et al 2020). Potential applications are countless with a huge impact on the quality of life (Chen et al 2012).…”