Optofluidic Formaldehyde Sensing: Towards On-Chip Integration

Abstract

<jats:p>Formaldehyde (HCHO), a chemical compound used in the fabrication process of a broad range of household products, is present indoors as an airborne pollutant due to its high volatility caused by its low boiling point ( T = − 19 °C). Miniaturization of analytical systems towards palm-held devices has the potential to provide more efficient and more sensitive tools for real-time monitoring of this hazardous air pollutant. This work presents the initial steps and results of the prototyping process towards on-chip integration of HCHO sensing, based on the Hantzsch reaction coupled to the fluorescence optical sensing methodology. This challenge was divided into two individually addressed problems: (1) efficient airborne HCHO trapping into a microfluidic context and (2) 3,5–diacetyl-1,4-dihydrolutidine (DDL) molecular sensing in low interrogation volumes. Part (2) was addressed in this paper by proposing, fabricating, and testing a fluorescence detection system based on an ultra-low light Complementary metal-oxide-semiconductor (CMOS) image sensor. Two three-layer fluidic cell configurations (quartz–SU-8–quartz and silicon–SU-8–quartz) were tested, with both possessing a 3.5 µL interrogation volume. Finally, the CMOS-based fluorescence system proved the capability to detect an initial 10 µg/L formaldehyde concentration fully derivatized into DDL for both the quartz and silicon fluidic cells, but with a higher signal-to-noise ratio (SNR) for the silicon fluidic cell ( S N R s i l i c o n = 6.1 ) when compared to the quartz fluidic cell ( S N R q u a r t z = 4.9 ). The signal intensity enhancement in the silicon fluidic cell was mainly due to the silicon absorption coefficient at the excitation wavelength, a ( λ a b s = 420 nm ) = 5 × 10 4 cm − 1 , which is approximately five times higher than the absorption coefficient at the fluorescence emission wavelength, a ( λ e m = 515 nm ) = 9.25 × 10 3 cm − 1 .</jats:p>

On-Line Gaseous Formaldehyde Detection Based on a Closed-Microfluidic-Circuit Analysis

“…Such improvement could also reduce the price of the detection module by approximately ten when produced in large series. So far, no study and even the very recent work of Mariuta et al (2020) [49], using the same derivative reagent to detect formaldehyde in liquid solution, was able to reach a satisfactory sensitivity using on-chip integration. Indeed, Mariuta et al (2020) showed that the sensitivity reached is approximately 100 times less so than that reported in this work, which is still very insufficient to allow precise and sufficiently rapid quantification of gaseous formaldehyde in the recirculation configuration.…”

Adsorption of gaseous formaldehyde on Y zeolites and on metal-organic frameworks

“…Its ubiquitous nature, its occurrence in indoor environments and its impact on human health make formaldehyde of great societal and scientific interest [8,18,[25][26][27][28]. Scientists are continuing to develop measurement methods for this pollutant and in particular real-time instruments such as analysers [29][30][31][32][33][34][35][36] and sensors [37][38][39][40][41][42] for monitoring indoor air. In addition, low cost indoor air quality measurement devices are now available for individuals willing to improve the quality of the air they breathe [43,44].…”

“…A second difficulty relies on the measurement of formaldehyde in the gas phase by means of a high-performance analytical instrument able to monitor the concentration in real time. Although several analytical methods are reported in the literature, most of them [29][30][31][32][33][34][35][36], including sensors [37][38][39][40][41][42], are only reliable to measure high concentrations because of their limited sensitivity. Due to these aforementioned technical constraints, most of the studies have been carried out at high formaldehyde concentrations (1 to 150 ppm) [50][51][52][53][54] which are not representative of the concentrations encountered in indoor environments.…”

Development of a Portable and Modular Gas Generator: Application to Formaldehyde Analysis

“…To overcome this drawback for gaseous formaldehyde quantification, the current trend in this analytical field is to develop real-time measurement tools such as sensors [30][31][32][33][34][35], analysers [36][37][38] or even microanalyzers [14,[39][40][41][42]. Chemical sensors are based on various gas detection mechanisms [43], namely resistive/chemoresistive, electrochemical, metaloxide-semiconductor field effect transistors (MOSFET), optical (surface plastic resonance (SPR)) and surface acoustic.…”