A gold nanoparticle-based colorimetric mercury(II) biosensor using a DNA probe with phosphorothioate RNA modification and exonuclease III-assisted signal amplification

Smart enzyme catalysts capable of self-separation by sensing the reaction extent

A smart biocatalyst should dissolve homogeneously for catalysis and recover spontaneously at the end of the reaction. In this study, we present a strategy for preparing self-precipitating enzyme catalysts by exploiting reaction-induced pH decreases, which connect the reaction extent to the catalyst aggregation state. Using poly(methacrylic acid)-functionalized gold nanoparticles as carriers, we construct smart catalysts with three model systems, including the glucose oxidase (GOx)-catalase (CAT) cascade, the alcohol dehydrogenase (ADH)-glucose dehydrogenase (GDH) cascade, and a combination of two lipases. All smart catalysts can self-separate with a nearly 100% recovery efficiency when a certain conversion threshold is reached. The threshold can be adjusted depending on the reaction demand and buffer capacity. By monitoring the optical signals caused by the dissolution/precipitation of smart catalysts, we propose a prototypic automation system that may enable unsupervised batch/fed-batch bioprocessing.

Colorimetric detection of mercury (Hg2+) using UV-vis spectroscopy and digital image analysis based on gold nanoparticles functionalized with bromelain enzyme

A very sensitive and selective colorimetric biosensor for the measurement of mercury ion (Hg2+) in environmental samples has been developed using functionalized gold nanoparticles with bromelain enzyme (brn-AuNPs). This work has shown that Hg2+ measurement based on spectrophotometer and digital image analysis is a very innovative and successful method for providing an effective preliminary system and has promise for the future of water quality biomonitoring. Response Surface Methodology (RSM), a Box-Behnken design-based technique, was used to identify the optimum levels of functionalization of bromelain to AuNPs. The created model's validity was confirmed, and statistical analysis revealed that the ideal functionalize conditions were 1 mM of AuNPs, functionalize with 0.59 mM bromelain concentration on 14 ℃ temperature and 72 h incubation time. The lowest colorimetric detection concentration (LOD) of brn-AuNPs of Hg2+ was 0.0092 ppm and 0.011 ppm for spectrophotometer and digital image analysis. As shown, digital image analysis had advantages based on the LOD result comparable to UV-VIS spectrophotometer. The practical application of the brn-AuNPs sensing was proven with mercury determination in water samples. The present study developed a robust sensor, which successfully implemented in a compact portable sensor kit, turning this sensor into a very potent tool for the development water quality biomonitoring system of Hg2+ application.

Rapid and highly selective colorimetric detection of mercury(II) ions in water sources based on a ribavirin functionalized AuNP sensor

Solvated mercuric ions (Hg²⁺), a toxic and harmful water pollutant, can easily accumulate in organisms and cause serious damage to the kidney, liver, and central nervous system. To realize rapid and efficient detection of mercury (II) ions in water sources, a kind of new colorimetric sensor of gold nanoparticles (AuNPs) functionalized with ribavirin (Rib-AuNPs) was proposed and characterized by TEM, DLS, XRD, and UV-vis in this work. The color of the Rib-AuNP solution rapidly changed from wine-red to gray-blue with the addition of Hg²⁺ based on the aggregation mechanism. The limits of detection (LODs) are 0.20 μM by the naked eye and 3.64 nM by UV-vis spectroscopy with a fine linear relationship in the range of 0-0.25 μM (R² = 0.9834) and 0.25-0.80 μM (R² = 0.9893) of Hg²⁺, indicating that the detection system of Rib-AuNPs could be applied to analyze Hg²⁺ with excellent selectivity and anti-interference in real water samples.

A functional peptide-mediated colorimetric assay for mercury ion based on dual-modified gold nanoparticles

In the work, a rapid and accurate biosensor for mercury ions (Hg²⁺) was constructed, with which aggregation of dual-modified (DGPFHR- and CALNN-) gold nanoparticles (D/C-AuNPs) could be triggered by the high specificity of peptides to Hg²⁺. The given peptide DGPFHR possesses great capability of capturing Hg²⁺, accompanied by the conformational folding. Under the circumstances, D/C-AuNPs were employed as the detection probes to accomplish the quantitative analysis of Hg²⁺. This is primarily because the specific Hg²⁺-induced folding of peptides reduces the electrostatic repulsion and steric hindrance, thus accelerating the AuNPs aggregation. The principle and application potential of this proposal was proved by evidence. And the results demonstrated that Hg²⁺ ions could be selectively detected as low as 28 nM with a linear range of 100-800 nM. In consideration of superior simplicity, selectivity, accuracy and stability, the protocol was advantageous over other projects in practical measurement of various water samples.

Ultrasensitive colorimetric strategy for Hg2+ detection based on T-Hg2+-T configuration and target recycling amplification

A novelty aptasensor for ultrasensitive detection of Hg²⁺ is developed, exploiting the combination of plasmonic properties of gold nanoparticles (AuNPs) and exonuclease III (Exo III)-assisted target recycling for signal amplification. In the presence of Hg²⁺, a DNA duplex can be formed due to the strong coordination of Hg²⁺ and T bases of single-stranded DNA (ssDNA) probe. Exo III digests the DNA duplex from the 3' to 5' direction, resulting in the releasing of Hg²⁺. Then, the released Hg²⁺ binds with another ssDNA probe through T-Hg²⁺-T coordination. After Exo III-assisted Hg²⁺ cycles, numerous ssDNA probes are exhausted, which promotes poly(diallyldimethylammonium chloride) (PDDA)-induced AuNP aggregation, leading to an obvious color change and aggregation-induced plasmon red shift of AuNPs (from 520 to 610 nm). Therefore, this biosensor is ultrasensitive, which is applicable to the detection of trace level of Hg²⁺ with a linear range from 5 pM to 0.6 nM and an ultralow detection limit of 0.2 pM. Furthermore, it enables visual detection of Hg²⁺ as low as 50 pM by the naked eye. More importantly, the assay can be applied to the reliable determination of spiked Hg²⁺ in sea water samples with good recovery.

TEMPO-Cellulose Nanocrystal-Capped Gold Nanoparticles for Colorimetric Detection of Pathogenic DNA

Nanocellulose-assisted gold nanoparticles are considered promising materials for developing eco-friendly diagnostic tools for biosensing applications. In this study, we synthesized 2,2,6,6-tetramethylpiperidin-1-piperidinyloxy (TEMPO)-oxidized cellulose nanocrystal (TEMPO-CNC)-capped gold nanoparticles (AuNPs) for the colorimetric detection of unamplified pathogenic DNA oligomers of methicillin-resistant Staphylococcus aureus. The fabricated TEMPO-CNC-AuNPs (TC-AuNPs) were characterized using UV-visible spectroscopy, transmission electron microscopy, atomic force microscopy, and dynamic light scattering. The average diameter of the synthesized AuNPs was approximately 30 nm. The aqueous solution of TC-AuNPs was stable and exhibited an absorption peak at 520 nm. The chemical interaction between TC-AuNPs and the surface charge of the target and non-target DNA determined the colorimetric differences under ionic conditions. A dramatic color change (red → blue) was observed in the TC-AuNP solution with the target DNA under ionic conditions due to the aggregation of AuNPs. However, no observable color change occurred in the TC-AuNP solution with the non-target DNA under similar conditions owing to the better shielding effects of the charged moieties. The colorimetric detection limit of the TC-AuNPs was demonstrated to be as low as 20 fM pathogenic DNA. Therefore, the use of TEMPO-oxidized CNC-capped AuNPs is efficient and straightforward as a biosensor for the colorimetric detection of pathogenic DNA.

l-Cysteine modified silver nanoparticles-based colorimetric sensing for the sensitive determination of Hg2+ in aqueous solutions

A simple and sensitive colorimetric sensing method was constructed for detection of Hg²⁺ in aqueous solutions and based on silver nanoparticles functionalized with l-cysteine (l-Cys-Ag NPs). In this method, adenosine triphosphate (ATP) induced aggregation of l-Cys-Ag NPs. Simultaneously, the solution colour changed from bright yellow to brown. In the presence of Hg²⁺ , Hg²⁺ chelated ATP to form a complex and reduce the degree of aggregation of l-Cys-Ag NPs and was accompanied by a colour change from brown to bright yellow. The changing values of absorbance at 390 nm were linearly correlated with concentration of Hg²⁺ over the 4.00 × 10^-8 to 1.04 × 10^-6 mol·L^-1 range, with a detection limit of 8 nM. This method was used successfully for detection of Hg²⁺ in real water samples and performed good selectivity and sensitivity. The recovery range was 91.5-109.1%, indicating that the method has vast application potential for determination of Hg²⁺ in the environment.