Design and synthesis of target-responsive hydrogel for portable visual quantitative detection of uranium with a microfluidic distance-based readout device

Abstract

Due to uranium's increasing exploitation in nuclear energy and its toxicity to human health, it is of great significance to detect uranium contamination. In particular, development of a rapid, sensitive and portable method is important for personal health care for those who frequently come into contact with uranium ore mining or who investigate leaks at nuclear power plants. The most stable form of uranium in water is uranyl ion (UO2(2+)). In this work, a UO2(2+) responsive smart hydrogel was designed and synthesized for rapid, portable, sensitive detection of UO2(2+). A UO2(2+) dependent DNAzyme complex composed of substrate strand and enzyme strand was utilized to crosslink DNA-grafted polyacrylamide chains to form a DNA hydrogel. Colorimetric analysis was achieved by encapsulating gold nanoparticles (AuNPs) in the DNAzyme-crosslinked hydrogel to indicate the concentration of UO2(2+). Without UO2(2+), the enzyme strand is not active. The presence of UO2(2+) in the sample activates the enzyme strand and triggers the cleavage of the substrate strand from the enzyme strand, thereby decreasing the density of crosslinkers and destabilizing the hydrogel, which then releases the encapsulated AuNPs. As low as 100nM UO2(2+) was visually detected by the naked eye. The target-responsive hydrogel was also demonstrated to be applicable in natural water spiked with UO2(2+). Furthermore, to avoid the visual errors caused by naked eye observation, a previously developed volumetric bar-chart chip (V-Chip) was used to quantitatively detect UO2(2+) concentrations in water by encapsulating Au-Pt nanoparticles in the hydrogel. The UO2(2+) concentrations were visually quantified from the travelling distance of ink-bar on the V-Chip. The method can be used for portable and quantitative detection of uranium in field applications without skilled operators and sophisticated instruments.

Smart Photonic Crystal Hydrogel Material for Uranyl Ion Monitoring and Removal in Water

“…Although the sensitivity of this material is not higher than some highly sensitive methods,[4g,17] the main advantage of this PCH material is that it can be used for visual and on‐site monitoring of UO 2 2+ without any additional signal molecules. In addition, the lowest detectable concentration of this material is lower than the maximum tolerable concentration of UO 2 2+ in the drinking water (130 × 10 −9 m ) established by the U.S. Environmental Protection Agency (EPA) …”

Colorimetric Detection of Uranyl Using a Litmus Test

“…Another key advantage is the modularity of the design, which allows for easy reconfiguration of the system into a new biosensor for detection of a different target with the use of a new DNAzyme that recognizes this target. In fact, many RNA-cleaving DNAzymes have been derived to specifically recognize diverse metal ions (McGhee et al, 2017 ), such as Pb 2+ (Breaker and Joyce, 1994 ; Santoro and Joyce, 1997 ), Zn 2+ (Li, 2000 ; Santoro et al, 2000 ), Mg 2+ (Breaker and Joyce, 1995 ; Santoro and Joyce, 1997 ), Ca 2+ (Faulhammer and Famulok, 1996 ; Zhou et al, 2016c ), Na + (Torabi et al, 2015 ), Hg 2+ (Hollenstein et al, 2008 ), Cd 2+ (Huang and Liu, 2015 ), Cr 3+ (Huang et al, 2016 ), Ln 3+ (Huang et al, 2014a , b , 2015 ), Ce 3+ (Zhou et al, 2016a ), and Ag + (Saran et al, 2017 ). In theory, the design featured in this study can be reconfigured for these DNAzymes and any other future RNA-cleaving DNAzyme to be derived for a target of interest.…”

“…Furthermore, 39E has been utilized for imaging of uranyl in live cells (Wu et al, 2013 ), and has been coupled to a contrast agent for magnetic resonance imaging (Xu et al, 2013 ). 39E has also been used in a variety of colorimetric detection assays, which employed both enzymatic (e.g., peroxidase) and non-enzymatic [e.g., gold nanoparticle (AuNP)] signal generation methods (Lee et al, 2008 ; Luo et al, 2012 ; Huang et al, 2016 ; Zhang et al, 2016 , 2017 ; Cheng et al, 2017 ; Yun et al, 2018 ). These enzymatic approaches utilize peroxidase, or peroxidase-mimetic components, while the non-enzymatic AuNP-based signal generation strategies largely rely on aggregation-dependent differences in AuNP absorbance to produce a visible signal.…”

DNA hydrogel-empowered biosensing

“…Using this method, cocaine could be detected at a concentration lower than 1 μM [76] and was additionally used for the detection of other targets such as ochratoxin A [77] and Aflatoxin B1 in beer, with a limit of detection of 1.77 nm [78]. Furthermore, in other similar work, the detection of uranium and lead were reported by utilizing a DNAzyme-substrate complex instead of the aptamer structure [79,80].…”