Highly Sensitive Strategy for Hg²⁺ Detection in Environmental Water Samples Using Long Lifetime Fluorescence Quantum Dots and Gold Nanoparticles

The authors herein described a time-gated fluorescence resonance energy transfer (TGFRET) sensing strategy employing water-soluble long lifetime fluorescence quantum dots and gold nanoparticles to detect trace Hg²⁺ ions in aqueous solution. The water-soluble long lifetime fluorescence quantum dots and gold nanoparticles were functionalized by two complementary ssDNA, except for four deliberately designed T–T mismatches. The quantum dot acted as the energy-transfer donor, and the gold nanoparticle acted as the energy-transfer acceptor. When Hg²⁺ ions were present in the aqueous solution, DNA hybridization will occur because of the formation of T–Hg²⁺–T complexes. As a result, the quantum dots and gold nanoparticles are brought into close proximity, which made the energy transfer occur from quantum dots to gold nanoparticles, leading to the fluorescence intensity of quantum dots to decrease obviously. The decrement fluorescence intensity is proportional to the concentration of Hg²⁺ ions. Under the optimum conditions, the sensing system exhibits the same liner range from 1 × 10^–9 to 1 × 10^–8 M for Hg²⁺ ions, with the detection limits of 0.49 nM in buffer and 0.87 nM in tap water samples. This sensor was also used to detect Hg²⁺ ions from samples of tap water, river water, and lake water spiked with Hg²⁺ ions, and the results showed good agreement with the found values determined by an atomic fluorescence spectrometer. In comparison to some reported colorimetric and fluorescent sensors, the proposed method displays the advantage of higher sensitivity. The TGFRET sensor also exhibits excellent selectivity and can provide promising potential for Hg²⁺ ion detection

Differentially expressed genes of each library compared with CK.

<p>Unigenes changed at transcriptional level following bacterial challenge were identified by filtering of the one-fold up- and down-regulated ones with FDR≤0.001.</p

Classification of the gene ontology (GO) for the <i>M. domestica</i> transcriptome.

<p>7,063 unigenes (26.1% of total) were categorized into 48 function groups.</p

Classification of the clusters of orthologous groups (COG) for the <i>M. domestica</i> transcriptome.

<p>8,549 unigenes (31.6% of the total annotated unigenes) were divided into 25 specific categories.</p

Gene counts belonging to immunity-related gene families.

a<p>Number of gene sequences from data of Christophides et al. (2002) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0104867#pone.0104867-Christophides1" target="_blank">[57]</a>, Evans et al. (2006) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0104867#pone.0104867-Evans1" target="_blank">[7]</a>, Tanaka et al. (2008) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0104867#pone.0104867-Tanaka1" target="_blank">[2]</a>.</p>b<p>Number of gene sequences obtained in this study that annotated with NCBI nr database.</p><p>* Two novel antimicrobial peptides identified and named in present study.</p

Summary of the <i>M. domestica</i> transcriptome.

<p>Summary of the <i>M. domestica</i> transcriptome.</p

Antibacterial activities of muscin and domesticin.

<p>MICs are expressed as the interval a–b, where a is the highest concentration tested at which microorganisms are growing and b the lowest concentration that causes 100% growth inhibition.</p

Statistics of gene expression sequencing.

<p>Statistics of gene expression sequencing.</p