Efficient ratiometric fluorescence probe utilizing silicon particles/gold nanoclusters nanohybrid for “on-off-on” bifunctional detection and cellular imaging of mercury (II) ions and cysteine

Captivating nano sensors for mercury detection: a promising approach for monitoring of toxic mercury in environmental samples

Mercury, a widespread highly toxic environmental pollutant, poses significant risks to both human health and ecosystems. It commonly infiltrates the food chain, particularly through fish, and water resources via multiple pathways, leading to adverse impacts on human health and the environment. To monitor and keep track of mercury ion levels various methods traditionally have been employed. However, conventional detection techniques are often hindered by limitations. In response to challenges, nano-sensors, capitalizing on the distinctive properties of nanomaterials, emerge as a promising solution. This comprehensive review provides insight into the extensive spectrum of nano-sensor development for mercury detection. It encompasses various types of nanomaterials such as silver, gold, silica, magnetic, quantum dot, carbon dot, and electrochemical variants, elucidating their sensing mechanisms and fabrication. The aim of this review is to offer an in-depth exploration to researchers, technologists, and the scientific community, and understanding of the evolving landscape in nano-sensor development for mercury sensing. Ultimately, this review aims to encourage innovation in the pursuit of efficient and reliable solutions for mercury detection, thereby contributing to advancements in environmental protection and public health.

A ratiometric fluorescent probe with a large Stokes shift for the detection of Hg2+ and its applications in environmental sample and living system analysis

Toxic mercury ions (Hg2+) can cause serious environmental pollution and accumulate in living organisms via the food chain. Therefore, monitoring Hg2+ is crucial in ensuring the safety of ecosystems and organisms. In this work, a novel ratiometric fluorescent probe CMT (5-(4-(diphenylamino)phenyl)-1-(7-hydroxy-coumarin-3-yl)-4-pentene-1,3-dione) based on coumarin was developed for detecting Hg2+, which displayed obvious fluorescence changes, a low detection limit (2.24 × 10-7 M), good selectivity, and a large Stokes shift (255 nm). The CMT probe could detect Hg2+ in real environmental soil and water samples. Furthermore, the CMT probe enabled the naked-eye detection of Hg2+ using test paper experiments. CMT was also applied for fluorescence imaging in living zebrafish and plants. This work provides a highly efficient tool for monitoring Hg2+ in environmental samples and biological systems.

Aggregation-caused dual-signal response of gold nanoclusters for ratiometric optical detection of cysteine

Designing ratiometric sensors for cysteine (Cys) monitoring with high accuracy is of great significance for disease diagnosis and biomedical studies. The current ratiometric methods mainly rely on multiplex probes, which not only complicates the operation but also increases the cost, making it difficult for quantitative Cys detection in resource-limited areas. Herein, one-pot prepared gold nanoclusters (Au NCs) that glow red fluorescent were synthesized by employing glutathione as the stabilizer and reducing agent. When Fe3+ is present with Au NCs, the fluorescence is quenched and the scattering is strong because of the aggregation of Au NCs. With introduction of Cys, Cys can efficiently compete with glutathione-modified Au NCs for Fe3+, which leads to increase of fluorescence and decrease of scattering. The ratiometric determination of Cys can be thereby realized by collecting the fluorescence and SRS spectrum simultaneously. The linear range for Cys was 5-30 µM with a detection limit of 1.5 µM. In addition, the sensing system exhibits good selectivity for Cys and shows potential application in biological samples.

A fluorescent probe based on aptamer gold nanoclusters for rapid detection of mercury ions

The mercuric ion (Hg2+) is a hazardous pollutant that is widely distributed in living organisms, foods, and environments with highly toxic and bio-accumulative properties. In the present study, a fluorescent probe based on aptamer gold nanoclusters (apt-AuNCs) was prepared for the ultrasensitive detection of Hg2+ in food. The principle underlying the prepared probe was the quenching of the fluorescence of apt-AuNCs in the presence of Hg2+ due to the strong metallophilic interactions between the 5d10 centers of Hg2+ and Au+. Under optimal conditions, the proposed fluorescent probe exhibited a linear relationship with Hg2+ concentration within the range of 2-200 nM (R2 = 0.9960). In addition, the limit of detection (LOD) was 0.0158 nM, which is below the Chinese standard value of 25 nM for Hg2+ in food. Furthermore, the apt-AuNCs were applied to detect Hg2+ in spinach and crawfish samples, with recovery percentages of 91.99%∼108.06%, meaning that apt-AuNCs could be used as a promising probe to detect Hg2+ in complex food samples.

Silicon Nanoparticle-Based Ratiometric Fluorescence Probes for Highly Sensitive and Visual Detection of VB2

In this work, blue fluorescent silicon nanoparticles (SiNPs) were prepared by a simple one-step hydrothermal method using (3-aminopropyl) triethoxy silane (APTES) and eriochrome black T as raw materials. The SiNPs showed favorable water solubility, thermal stability, pH stability, salt tolerance, and photobleaching resistance. At an excitation wavelength of 376 nm, the SiNPs emitted bright blue fluorescence at 460 nm. In the presence of vitamin B₂ (VB₂), the fluorescence intensity (FL intensity) of the SiNPs at 460 nm decreased obviously, and a new peak appeared at 521 nm. Based on this, a novel ratiometric fluorescence method was established for VB₂ detection. There was a good linear relationship between the fluorescence intensity ratio (F ₅₂₁/F ₄₆₀) and VB₂ concentration from 0.5 to 60 μM with a detection limit of 135 nM. This method was successfully applied to detect VB₂ content in the samples of vitamin B₂ drugs and beverages. Additionally, a simple paper sensor based on the SiNPs was designed to visualize detection of VB₂. With the support of color recognition software on a smartphone, the visual quantitative analysis of VB₂ was realized, ranging from 40 to 800 μM.

A novel sensor for visual and selective detection of Hg2+ based on functionalized doped quantum dots

In this paper, a novel analytical platform for the visual, sensitive and reliable analysis of mercury ions (Hg²⁺) is fabricated based on functionalized doped quantum dots. We synthesized a new specific nano-material, zinc dithiothreitol combined with graphene quantum dots (ZnNCs-NGQDs), by a simple and convenient method which, as an efficient luminophore, was then applied to construct an electrochemiluminescence (ECL) system for the first time. Under optimized conditions, the ECL sensor showed an excellent response for Hg²⁺ in the linear range of 1.0 mM to 10 pM, with a low detection limit of 3 pM. Moreover, the proposed method demonstrated satisfactory selectivity, stability and acceptable reproducibility for the detection of Hg²⁺. The recovery of tap water and lake water samples ranged from 96% to 105%, indicating the potential applicability of the proposed method for monitoring environmental water samples. Meanwhile, visual attempts for mercury ion detection by using doped quantum dots have also obtained satisfactory results. Importantly, our research revealed a viable method for improving the sensitivity and convenience of target studies in sensing fields derived from functional material design.

A fluorescent organic nanoparticles-based sensor synthesized through hydrothermal process and its application in sensing Hg2+ of real samples and fast visual detection

The fluorescent organic nanoparticles (FONs)-based sensor has been attracting great attention in recent years. There are still big challenges in the preparation and application of FONs-based sensor. In this study, a FONs-based sensor was designed and developed through facile hydrothermal process using 3-perylenecarboxaldehyde (PlCA) as the fluorophore and L-methionine (Met) as the recognition site for mercury ions. According to the experimental results, the fluorescence intensity of the as-prepared PlCA-M would decrease when adding Hg²⁺ and the mechanism was extrapolated to be photoinduced electron transfer inducing by specific coordination interaction. The acquired PlCA-M-based sensor was used to monitor Hg²⁺ in several real samples (environmental water, tea, and apple) with the limit of detection being 60 nM. Remarkably, a visual detection device based on FONs, SDS-PAAG (sodium dodecyl sulfate polyacrylamide gel) @PlCA-M was firstly constructed and successfully used to Hg²⁺ semi-quantitation by naked eyes. In addition, the acquired FONs was applied into imaging tool for security information detection and identified as solid-state luminescent material for the first time.

Silicon nanoparticles / gold nanoparticles composite as a fluorescence probe for sensitive and selective detection of Co2+ and vitamin B12 based on the selective aggregation and inner filter effect

Cobalt as a transition metal ion is a biologically essential trace element, and plays an important role in various biological systems. The silicon nanoparticles (SiNPs) / gold nanoparticles (AuNPs) composite as a simple and efficient fluorescent probe was developed to detect Co²⁺ and vitamin B₁₂ (VB₁₂) based on the selective aggregation and inner filter effect (IFE). The green-emitting SiNPs were synthesized by one-pot hydrothermal method, and the AuNPs were synthesized and modified with thioglycolic acid and cetyltrimethylammonium bromide. The fluorescent probe was fabricated by simple mixing the SiNPs and AuNPs together. In the presence of Co²⁺/VB₁₂, AuNPs are selectively aggregated, which results in the enhancement of the local surface plasmon resonance absorption centered at 520 nm and the green fluorescence of SiNPs is significantly quenched via IFE. The fluorescence quenching efficiency of the probe is linearly proportional to the concentration of Co²⁺ in the range of 0.1-80 µM with a low detection limit of 60 nM, which is far lower than the guideline value of Co²⁺ in drinking water (1.7 µM). For vitamin B₁₂ (VB₁₂), its linear relationship is in the range of 0.1-100 µM, and the limit of detection is 69 nM. Furthermore, the proposed method shows good selectivity for the detection of Co²⁺ and VB₁₂, and does not need sophisticated pretreatment, only through simple filter. It has been applied in actual environmental water samples and drug tablets with satisfactory results.

A facile and total water-soluble fluorescent organic nanoparticles-based sensor for Hg2+ detection and its application in tea samples

In this study, a novel FONs-based sensor P-M(w) was synthesized using 1-Pyrenecarboxaldehyde and L-methionine through facile hydrothermal strategy. The fluorescence emission peaks of the acquired P-M(w) would show specific changes after the addition of Hg²⁺ due to interfering the PET process and inducing nano-structure conformational rigidification of P-M(w). Notably, the water-soluble FONs-based sensor was firstly used to detect Hg²⁺ in tea samples providing a new material choice for the fluorescence sensor construction of metal ion detection. Besides, the qualitative and quantitative analysis of Hg²⁺ could be carried out with P-M (w) at a very low concentration (1 μg/mL) meaning that the acquired P-M(w) synthesized by few grams of reactants may satisfy the detection of approximate fifty thousand samples.

Rational design of multi-functional thermally activated delayed fluorescence emitters for both sensor and OLED applications

Non-conjugated linking as a molecular design strategy to construct multifunctional structures to achieve the TADF feature and sensor properties in a single system.

Ratiometric fluorescent sensor based on MoS2 QDs and AuNCs for determination and bioimaging of alkaline phosphatase

Herein, a ratiometric fluorescent sensor based on MoS₂ quantum dots (QDs) and glutathione-capped gold nanoclusters (AuNCs) was developed for determination and imaging of alkaline phosphatase (ALP). The sensor was developed by covalently linking QDs with AuNCs to form stable MoS₂@AuNCs nanohybrids that exhibited the blue fluorescence of MoS₂ QDs and the red fluorescence of AuNCs. In the presence of Ce³⁺, the fluorescence intensity of AuNCs was increased due to the aggregation-induced emission enhancement (AIEE), while that of MoS₂ QDs remained unchanged, thus could be used as a reference signal. After adenosine 5'-monophosphate (AMP) and ALP were introduced into the system, AMP was hydrolyzed to adenosine and phosphate ions (PO₄^3-). Owing to higher affinity between Ce³⁺ and PO₄^3-, the AIEE effect was inhibited, in turn resulting in the decrease of AuNCs fluorescence. The developed ratiometric fluorescent sensor had a linear response to ALP concentration ranging from 0.5 to 50 U L^-1 with a detection limit (LOD) of 0.08 U L^-1. Moreover, the sensor had low cytotoxicity and was successfully employed in lysosome localization and bioimaging of intracellular ALP in living cells.

A highly selective ratiometric fluorescent probe for doxycycline based on the sensitization effect of bovine serum albumin

Fluorescent probes with in-situ visual feature have received numerous attentions for detecting doxycycline (DC), a semisynthetic tetracycline antibiotic widely used in animal husbandry. However, reported fluorescent probes commonly fail to selectively detect DC among tetracycline antibiotics due to their structural similarity. In this work, bovine serum albumin-capped gold nanoclusters (BSA-AuNCs) were ingeniously used as the ratiometric fluorescent probe for detecting DC over other tetracycline antibiotics through the selective sensitization effect of BSA on DC. After adding DC, the red fluorescence of BSA-AuNCs almost remained unchanged, while the green fluorescence of DC also emerged under the sensitization of BSA. BSA-AuNCs showed the highest response toward DC among tetracycline antibiotics ascribed to the strongest sensitization effect of BSA on DC. BSA-AuNCs also displayed the features of simple synthesis, short response time (1 min) and low detection limit (36 nM). BSA-AuNCs were finally applied to detecting DC in fish samples, and further fabricated into test strips for ease of carrying. Thus, this work proposes an efficient strategy to design fluorescent probe for selectively detecting DC among tetracycline antibiotics.

Nanomaterial-Based Dual-Emission Ratiometric Fluorescent Sensors for Biosensing and Cell Imaging

Owing to the unique optophysical properties of nanomaterials and their self-calibration characteristics, nanomaterial-based (e.g., polymer dots (Pdots) quantum dots (QDs), silicon nanorods (SiNRs), and gold nanoparticle (AuNPs), etc.) ratiometric fluorescent sensors play an essential role in numerous biosensing and cell imaging applications. The dual-emission ratiometric fluorescence technique has the function of effective internal referencing, thereby avoiding the influence of various analyte-independent confounding factors. The sensitivity and precision of the detection can therefore be greatly improved. In this review, the recent progress in nanomaterial-based dual-emission ratiometric fluorescent biosensors is systematically summarized. First, we introduce two general design approaches for dual-emission ratiometric fluorescent sensors, involving ratiometric fluorescence with changes of one response signal and two reversible signals. Then, some recent typical examples of nanomaterial-based dual-emission ratiometric fluorescent biosensors are illustrated in detail. Finally, probable challenges and future outlooks for dual-emission ratiometric fluorescent nanosensors for biosensing and cell imaging are rationally discussed.

Development of carbon dot-thiochrome-based sensing system for ratiometric fluorescence detection of D-penicillamine

A simple and rapid ratiometric fluorescent sensing system for D-penicillamine (D-PA) determination is developed based on yellow carbon dots (Y-CDs) combined with thiochrome (oxVB₁) for the first time. The oxidization of thiamine (VB₁) can be catalyzed by Alkaline-hydrolyzed artemisinin (a-ART) to form oxVB₁, which leads to the occurrence of fluorescence emission peak at 466 nm. Furthermore, the oxidation reaction between a-ART and VB₁ could be inhibited by D-PA, and accompanied with the decrease of fluorescence at 466 nm. However, the fluorescence peak of Y-CDs as an internal reference at 566 nm was almost unchanged. The ratiometric signal changes contributed to a robust and sensitive D-PA sensing. Under the optimal condition, a good linear response for the D-PA detection was obtained in the ranges of 0.5-50 μM with a detection limit of 0.33 μM. In addition, Y-CDs and thiochrome-based sensing system was applied to D-PA determination in real samples and obtained acceptable results. We developed a new carbon dots/thiochrome fluorescent nanoprobe for ratiometric fluorescence sensing of D-penicillamine.

A Review of Off-On Fluorescent Nanoprobes: Mechanisms, Properties, and Applications

With the development of nanomaterials, fluorescent nanoprobes have attracted enormous attention in the fields of chemical sensing, optical materials, and biological detection. In this paper, the advantages of "off-on" fluorescent nanoprobes in disease detection, such as high sensitivity and short response time, are attentively highlighted. The characteristics, sensing mechanisms, and classifications of disease-related target substances, along with applications of these nanoprobes in cancer diagnosis and therapy are summarized systematically. In addition, the prospects of "off-on" fluorescent nanoprobe in disease detection are predicted. In this review, we presented information from all the papers published in the last 5 years discussing "off-on" fluorescent nanoprobes. This review was written in the hopes of being useful to researchers who are interested in further developing fluorescent nanoprobes. The characteristics of these nanoprobes are explained systematically, and data references and supports for biological analysis, clinical drug improvement, and disease detection have been provided appropriately.

Microwave-assisted synthesis of fluorescent silicon quantum dots for ratiometric sensing of Hg (II) based on the regulation of energy transfer

The rapid and sensitive detection of Hg²⁺ is highly required to protect the environmental safety and human healthy. In the present work, a ratiometric fluorescent sensing platform, consisting of silicon quantum dots (SiQDs), Rox-labelled DNA (Rox-DNA), and Exonuclease III (Exo III), is developed for the accurate detection of Hg²⁺. As for fluorescent probe, we report the first use of glutathione as reduction reagent for the microwave synthesis of SiQDs, achieving the facile (using a house-hold microwave oven) and rapid (within 8 min) synthesis. Such SiQDs show pH-independent spectra and reversible fluorescent behavior with temperature. Moreover, experimental results revealed that the electrostatic interaction-induced aggregation of Rox-DNA and SiQDs facilitated the occurring of energy transfer (ET). And detection principle based on the regulation of ET between Rox and SiQDs with Exo III was designed for analysis. ET effect resulted in the fluorescent fading of Rox while that of SiQDs kept stable. For analysis, the addition of Hg²⁺ led to the formation of double-stranded Rox-DNA via T-Hg²⁺-T. Exo III would cut these double-stranded DNA to release Rox and Hg²⁺, thereby impeding the ET effect and recovering the fluorescent of Rox. Such SiQDs/Rox-DNA/Exo III ratiometric fluorescent sensing platform exhibited a linear response concentration range of 0.02 nM-10 nM with a detection limit of 0.01 nM. It was successfully used to analyze the water and soil samples. The reliability was validated by ICP-MS. Our work should promote the practical application of ratiometric fluorescent assay.

Redox-induced target-dependent ratiometric fluorescence sensing strategy and logic gate operation for detection of α-glucosidase activity and its inhibitor

A target-dependent ratiometric fluorescence sensing strategy was designed and fabricated based on a redox reaction for highly sensitive detection of α-glucosidase (α-Glu) activity and its inhibitor. In this study, silicon quantum dots (SiQDs) with excellent optical properties and two-dimensional (2D) cobalt oxyhydroxide (CoOOH) nanosheets were successfully prepared and exploited for the detection of analytes. The CoOOH nanosheets are able to oxidize o-phenylenediamine (OPD), and the product 2,3-diaminophenazine (oxOPD) not only quenches the blue fluorescence of SiQDs (440 nm) by the inner filter effect (IFE) but also emits orange fluorescence (565 nm). α-Glu can catalytically hydrolyze l-ascorbic acid-2-O-α-d-glucopyranosyl (AA2G) to produce ascorbic acid (AA). The redox between AA and CoOOH could lead to the damage of CoOOH nanosheets, thereby inhibiting the oxidization of OPD and effectively preserving the fluorescence of SiQDs. Thus, ratiometric detection of α-Glu activity was achieved according to the AA-dependent dual-fluorescence signal responses. Under the optimal conditions, good linearity was obtained in the range of 0.01-6 U mL-1 with a detection limit of 0.004 U mL-1. The IC50 of α-Glu inhibitor acarbose was estimated to be 0.216 μM. The method provides high sensitivity and selectivity for the determination of α-Glu activity and its inhibitor, which has great application potential in clinical diagnosis and anti-diabetic drug screening. Furthermore, a logic gate analytical device was successfully established based on double fluorescence signals, which makes it possible to monitor α-Glu activity by intelligence equipment.

Sensing of mercury ions in Porphyra by Copper @ Gold nanoclusters based ratiometric fluorescent aptasensor

A novel aptamer-modified Copper @ Gold nanoclusters (apt-Cu@Au NCs) based ratiometric fluorescent probe was developed for mercury ions (Hg²⁺) determination in Porphyra. The apt-Cu@Au NCs were well dispersed in solution without Hg²⁺ but combined together for the formation of thymidine-Hg-thymidine structure with the addition of Hg²⁺, which further caused the changes in their fluorescence intensities owing to fluorescence resonance energy transfer. Along with that, the changes in fluorescent colors are visible to the naked eye. Accordingly, Hg²⁺ were determined ranging from 0.1 to 9.0 μM by fluorescence analysis with the detection limit of 4.92 nM. Moreover, a homemade device utilizing smartphone and microfluidic chip was designed for colorimetric determination of Hg²⁺ ranging from 0.5 to 7.0 μM with good portability and usefulness. The proposed methods were used for Hg²⁺ detection in Porphyra with the recoveries of 101.83-114.00%, suggesting the considerable potential for evaluating Hg²⁺ levels in aquatic products.

Ratiometric fluorescence assay for L-Cysteine based on Fe-doped carbon dot nanozymes

In this work, a ratiometric fluorescence method based on nanozyme was fabricated to determine L-Cysteine. Taking silkworm feces as a carbon source, together with Fe³⁺, Fe-doped carbon dots (Fe-CDs) were synthesized through a hydrothermal method. Fe-CDs were able to oxidize the enzyme substrate o-phenylenediamine (OPD) to produce oxidized OPD (Ox-OPD) when H₂O₂ coexisted with them. Based on the fluorescence property of Fe-CDs and Ox-OPD, a dual-emission system was built. Since L-Cysteine contains reductive thiols that can inhibit the production of Ox-OPD, the addition of L-Cysteine caused a decrease in the fluorescence intensity of Ox-OPD. The results showed that the ratio of fluorescence intensities at 450 and 560 nm (I₄₅₀/I₅₆₀) varied linearly with the concentration of L-Cysteine in the range of 0.25-90 μM and the limit of detection is as low as 0.047 μM. Furthermore, using this ratiometric fluorescence system to determine L-Cysteine in serum and tap-water samples, average recoveries were evaluated to reach 98.75%-103.27% with the relative standard deviation of no more than 4.5%. Based on the fluorescence property and nanozyme-like activity, this work provides an inspiration to open a new horizon in using natural carbon source to synthesize CDs and for the application of CDs as a nanozyme.

Ligand-modulated aqueous synthesis of color-tunable copper nanoclusters for the photoluminescent assay of Hg(II)

Water-soluble Cu nanoclusters (NCs) with tunable emission were synthesized through an eco-friendly one-pot aqueous method. Blue-, green-, and red-emitting NCs with the emission peaks at 420 nm, 505 nm, and 630 nm were obtained by employing ethanediamine, cysteine, and glutathione as surface ligands, respectively. The ligand effects on the optical properties of Cu NCs were studied by the single variable method. It has been revealed by systematic characterizations that the dependence of emission color on the structures of ligands was mainly attributed to their different size-tuning effects. Glutathione has the strongest chelating ability and it can significantly reduce the monomer reactivity and thus decrease the supersaturation degree of the reaction, which is favorable for modulating Cu precursor to grow into larger NCs. In contrast, ethanediamine ligand resulted in smaller nanoclusters due to its weaker binding capability. Because of the strong emission and terrific fluorescent stability, Cu NCs capped with ethanediamine, possessing an emission peak at 420 nm when excited at a wavelength of 350 nm, were directly used for probing Hg(II) with satisfying selectivity, presenting a linear range of 0.1-5.0 mM and a detection limit of 33 μM. The sensor showed good performance in real sample analysis with recoveries ranging from 99% to 103%, and comparable accuracy with atomic fluorescence spectroscopy, manifesting the reliability of the current strategy for sensing Hg(II). Graphical abstract Water-soluble copper nanoclusters with blue, green, and red emissions were synthesized by employing ethanediamine, cysteine, and glutathione as surface ligands respectively, and the blue-emitting nanoclusters with strong emission and terrific stability were directly used for selectively sensing Hg²⁺.

Highly selective sensor for the detection of Hg2+ ions using homocysteine functionalised quartz crystal microbalance with cross-linked pyridinedicarboxylic acid

This study reports an insightful portable vector network analyser (VNA)-based measurement technique for quick and selective detection of Hg2+ ions in nanomolar (nM) range using homocysteine (HCys)-functionalised quartz-crystal-microbalance (QCM) with cross-linked-pyridinedicarboxylic acid (PDCA). The excessive exposure to mercury can cause damage to many human organs, such as the brain, lungs, stomach, and kidneys, etc. Hence, the authors have proposed a portable experimental platform capable of achieving the detection in 20-30 min with a limit of detection (LOD) 0.1 ppb (0.498 nM) and a better dynamic range (0.498 nM-6.74 mM), which perfectly describes its excellent performance over other reported techniques. The detection time for various laboratory-based techniques is generally 12-24 h. The proposed method used the benefits of thin-film, nanoparticles (NPs), and QCM-based technology to overcome the limitation of NPs-based technique and have LOD of 0.1 ppb (0.1 μg/l) for selective Hg2+ ions detection which is many times less than the World Health Organization limit of 6 μg/l. The main advantage of the proposed QCM-based platform is its portability, excellent repeatability, millilitre sample volume requirement, and easy process flow, which makes it suitable as an early warning system for selective detection of mercury ions without any costly measuring instruments.