Dip-and-Read, Organic Solvent-Compatible, Paper-Based Analytical Devices Equipped with Chromatographic Separation for Indole Analysis in Shrimp

Abstract

We developed an organic solvent-compatible paper-based analytical device (PAD) for the quantitative analysis of indole, which is an indicator of shrimp freshness. Although indole is insoluble in water, ethyl acetate is a suitable solvent to dissolve and extract indole from shrimp. The PADs are fabricated using a cutting method that allows the use of an organic solvent because no hydrophobic barrier is needed to form fluidic channels. Ehrlich’s reagent consists of 4-(dimethylamino)­benzaldehyde and p-dimethylaminobenzaldehyde and was deposited onto the reaction zone of the PAD followed by lamination to prevent evaporation of the ethyl acetate. Samples are introduced into the PAD via immersion in organic sample solutions. When the PAD is immersed into an indole solution of ethyl acetate in a closed bottle, the sample solution penetrates the channel of the PAD and successively flows into the detection zone to form a hydrophilic colored product. The PADs provide a linear relationship between the logarithm of the indole concentration and the color intensity within a range of 1.0–20 ppm with correlation coefficients of r 2 > 0.99. The limits of detection and quantification are 0.36 and 0.71 ppm, respectively. Relative standard deviations for both the intraday (n = 2) and interday (n = 3) precision were less than 2.5%. In the indole analysis of shrimp, the PADs separated the interfering orange-colored astaxanthin in the extract from the colored product of indole via the paper chromatographic principle. We used the PADs to investigate the degradation of shrimp, and the results showed a rapid increase in the indole level after 7 days. High-performance liquid chromatography verified the accuracy of the PADs by showing good agreement with the obtained indole levels.

An irreversible paper-based profluorescent nitroxide probe for the selective detection of ascorbic acid

“…The transformation of hydroxylamine 2 to O -acylalkoxyamine 3 could prevent reoxidation and provide better precision. In recent years, colorimetric paper strips or paper-based sensors have been extensively investigated as devices to quantify various analytes, such as heavy metals, 21 carcinogenic organic compounds present in food products, 22 carcinoembryonic antigens (a tumor marker), 23 dopamine, 24 cysteine 25 and other biologically relevant analytes 26 since they are easily handled. However, to the best of our knowledge, the quantitative analysis of AA on a paper-based sensor using profluorescent nitroxide probes has not been explored.…”

Deep Learning Used with a Colorimetric Sensor Array to Detect Indole for Nondestructive Monitoring of Shrimp Freshness

“…putrefaciens, respectively. Indole is a tryptophan-derived substance that appears in protein structure and can be broken down and metabolized by the tryptophanase enzyme found in some mesophilic bacteria . Color response of indicator arrays exposed at 10 3 CFU/mL of S.…”

“…The indole is a signal molecule to evaluate freshness of shrimp . The US Food and Drug Administration (FDA) categorized fresh shrimp as primary freshness within an indole concentration of no more than 25 μg/100 g, whereas indole concentration ≥25 μg/100 g was considered as secondary freshness and spoiled shrimp .…”

“…Indole is a tryptophan-derived substance that appears in protein structure and can be broken down and metabolized by the tryptophanase enzyme found in some mesophilic bacteria. 39 Color response of indicator arrays exposed at 10 3 CFU/mL of S. aureus, E. coli, P. fluorescens, and S. putrefaciens suspension after incubating at 37 °C for 12 h is revealed in Figure 5c. The strip sensor array achieved a change to pink or mulberry color, The indole is a signal molecule to evaluate freshness of shrimp.…”

Development of Pipetteless Paper-Based Analytical Devices with a Volume Gauge

“…Recently, several studies have demonstrated applications of the PADs to different types of food and environmental samples using detection schemes such as colorimetry, − electrochemistry, − fluorometry, − and chemiluminescence. − Colorimetry is the most frequently employed detection method because it is simple to achieve qualitative and quantitative analyses of analytes by observing the color change in the detection zones on the PAD. The color images are captured with a digital camera, smartphone, or scanner, which then is followed by image processing using software such as ImageJ. , …”