Microfluidic integrated gas sensors for smart analyte detection: a comprehensive review

Abstract

The utilization of gas sensors has the potential to enhance worker safety, mitigate environmental issues, and enable early diagnosis of chronic diseases. However, traditional sensors designed for such applications are often bulky, expensive, difficult to operate, and require large sample volumes. By employing microfluidic technology to miniaturize gas sensors, we can address these challenges and usher in a new era of gas sensors suitable for point-of-care and point-of-use applications. In this review paper, we systematically categorize microfluidic gas sensors according to their applications in safety, biomedical, and environmental contexts. Furthermore, we delve into the integration of various types of gas sensors, such as optical, chemical, and physical sensors, within microfluidic platforms, highlighting the resultant enhancements in performance within these domains.

Keywords: gas sensors; microfluidic; miniaturization; selectivity; sensitivity.

FIGURE 1

Number of papers on microfluidic gas sensor at different steps of filtration (Top) Number of papers based on application category (Bottom).

FIGURE 2

(A) Timeline view of the microfluidic gas sensor papers gathered for this review, (B) Geographical view of distribution of publications based on countries, and the correspondence authors.

FIGURE 3

The mechanism of the bubble-based gas sensor: the gas mixture is separated into its constituents by passing through a separation column. Then, having passed through a flow-focusing microchannel, different analytes will be categorized based on their bubble diameter (Bulbul and Kim, 2015b). Reprinted with permission from RSC.

FIGURE 4

The mechanism of the colorimetric gas sensor suggested by Tirandazi and Hidrovo (Tirandazi and Hidrovo, 2018): I) The liquid phase carrying reagent enters a flow focusing microchannel, where they will be mixed with the gas analytes, II) the formed droplets containing both analytes and reagents are gathering in a liquid medium, III) The formed droplets are then carried through a series of microchannels by the liquid carrier, where further analysis is conducted on them. Reprinted with permission from Elsevier.

FIGURE 5

The mechanism of the microfluidic SERS gas sensor, (A) The carrier liquid flows from the reservoir into the open microchannel, (B) Au nanoparticles adsorb analytes, which leads to the formation of Au aggregates function as SERS hotspots (Piorek et al., 2007). Reprinted with permission from PNAS.

FIGURE 6

(A–H) The results of SWNT-FETs characterizations tests and gas sensing properties (Lee et al., 2015b). Reprinted with permission from Elsevier.

FIGURE 7

(A) Image of the microfluidic gas detection system, (B) The calibration curves, (C) The short term stability study of the proposed setup (Martini et al., 2010). Reprinted with permission from Elsevier.

FIGURE 8

(A) Normalized response signals of the microfluidic gas sensor with tin oxide detector to seven different analytes with eight repetitions, (B) Schematic of the microfluidic gas sensor, and (C) The schematic of the sensing setup (Paknahad et al., 2019b). Reprinted with permission from Springer Nature.

FIGURE 9

(A) Schematic of the gas sensing device, (B) TEM images of SBA-15, SBA-16, SBA-15-acid, and CPG (Chatterjee et al., 2020). Reprinted with permission from RSC.

FIGURE 10

(A) FTIR spectra, (B) SEM photographs of synthesised MIP nanoparticles, (C) Results of the modified microfluidic gas sensor when exposed to 800 ppm of different VOCs (Janfaza et al., 2019a). Reprinted with permission from Springer Nature.

FIGURE 11

(A) Schematic of a basic MOS gas sensor, (B) Equivalent electrical circuit for the MOS sensor (Paknahad et al., 2017b). Reprinted with permission from Elsevier.

FIGURE 12

(A) Schematic representation of the sensor microchip fabrication (Raj et al., 2021a), (B) Fabrication of NO sensor (Cha et al., 2010). Reprinted with permission from ACS.