Recent advances and trends in innovative biosensor-based devices for heavy metal ion detection in food

Low-cost, reliable, and efficient biosensors are crucial in detecting residual heavy metal ions (HMIs) in food products. At present, based on distance-induced localized surface plasmon resonance of noble metal nanoparticles, enzyme-mimetic reaction of nanozymes, and chelation reaction of metal chelators, the constructed optical sensors have attracted wide attention in HMIs detection. Besides, based on the enrichment and signal amplification strategy of nanomaterials on HMIs and the construction of electrochemical aptamer sensing platforms, the developed electrochemical biosensors have overcome the plague of low sensitivity, poor selectivity, and the inability of multiplexed detection in the optical strategy. Moreover, along with an in-depth discussion of these different types of biosensors, a detailed overview of the design and application of innovative devices based on these sensing principles was provided, including microfluidic systems, hydrogel-based platforms, and test strip technologies. Finally, the challenges that hinder commercial application have also been mentioned. Overall, this review aims to establish a theoretical foundation for developing accurate and reliable sensing technologies and devices for HMIs, thereby promoting the widespread application of biosensors in the detection of HMIs in food.

Turn-On Solid-State Fluorescent Determination of Zinc Ion by Quinoline-Based Covalent Organic Framework

A new quinoline-based COF (covalent organic framework), obtained by Povarov reaction, containing 2,6-diisopropylphenyl moieties as substituents over the heterocyclic ring is described for detecting Zn2+ in aqueous solution. The introduction of the mentioned bulky phenyl rings into the network favors an increase of the distance between the reticular sheets and their arrangement, obtaining a new material with an alternating AB type stacking. The new material exhibits good selectivity to detect Zn2+ by fluorescence emission in aqueous solutions up to a concentration of 1.2 × 10-4 m of the metal ion. In order to have a deeper insight into the interaction between the COF and the zinc cation, a thorough spectroscopical, microscopical, and theoretical study is also presented and discussed in this communication.

Colorimetric detection of heavy metal ions with various chromogenic materials: Strategies and applications

Detection of heavy metal ions has drawn significant attention in environmental and food area due to their threats to the human health and ecosystem. Colorimetry is one of the most frequently-used methods for the detection of heavy metal ions owing to its simplicity, easy operation and rapid on-site detection. The development of chromogenic materials and their sensing mechanisms are the key research direction in the area of colorimetric method. Since each chromogenic material has their unique optical and chemical properties, they have totally different colorimetric sensing mechanisms. This review focuses on the chromogenic materials and their sensing strategies for the colorimetric detection of heavy metal ions. We divide the chromogenic materials into three types, including organic materials, inorganic materials, and other materials. As for each type of chromogenic material, we discuss their detailed sensing strategies, sensing performance, and real sample applications. Moreover, current challenges and perspectives related to the colorimetry of heavy metal ions are also discussed in this review. The aim of this review is to help readers to better understand the principles of colorimetric methods for heavy metal ions and push the development of rapid detection of heavy metal ions.

Developing a new chemosensor targeting zinc ion based on two types of quinoline platform

A chemosensor DQ (2-(2-(quinolin-2-yl)hydrazinyl)-N-(quinolin-8-yl)acetamide), based on two quinoline moieties, has been synthesized. DQ could detect zinc ion through fluorescence turn-on in aqueous media. Limit of detection was calculated as 0.07 μM, far lower than the standard of WHO for zinc ion. The practicality of DQ was demonstrated via the successful results of reusability with EDTA, easy detection on the test strip, and precise quantification in real water samples. Additionally, sensor DQ could be applied to bioimaging of zinc ion in zebrafish. Sensing process of zinc ion by DQ was studied through fluorescence and UV-Vis spectroscopy, ¹H NMR titration, and ESI-mass spectrometry.

Porous silica and polymer monolith architectures as solid-state optical chemosensors for Hg2+ ions

We demonstrate a simple strategy to concoct a competent solid-state opto-chemosensor for the selective and sensitive visual detection of Hg²⁺ ions. The sensor fabrication involves the utilization of indigenously prepared mesoporous silica and polymer monoliths as probe anchoring templates and 8-hydroxy-7-(4-n-butylphenylazo) quinoline (HBPQ) as the chromo-ionophoric probe for Hg²⁺ sensing. Both the monoliths are designed with discrete structural and morphological features to serve as efficient host templates. The structural and surface features of the monoliths are characterized using p-XRD, TEM, SEM, SAED, EDAX, XPS, and N₂ isotherm analysis. The synergetic features of monolith structural hierarchy along with the probe's selective chelating ability enable rapid signal response and remarkable ion selectivity for Hg²⁺. The solid-state sensors evince a linear signal response from 0.6 to 150 μg/L for Hg²⁺ recognition, with superior data authenticity and replication that is preceded by an RSD value of ≤ 2.25% when tested with real water samples.Graphical abstract Mesoporous silica and polymer monolith architects hosting HBPQ probe molecules demonstrate an excellent visual sensing of ultra-trace (μg/L) Hg²⁺ in various water samples with a striking color transition from light orange to dark red upon complexation of probe with Hg²⁺. The solid-state sensors are Hg²⁺ ion selective, super-responsive, real-time applicable, and also reusable.

Biogenic Silver Nanoparticles for Trace Colorimetric Sensing of Enzyme Disrupter Fungicide Vinclozolin

We report a novel, simple, efficient, and green protocol for biogenic synthesis of silver nanoparticles (AgNPs) in aqueous solution using clove (Syzygium aromaticum) extract as a reducing and protecting agent. Ultraviolet-visible (UV-Vis) spectroscopy was employed to monitor the localized surface plasmon resonance (LSPR) band of clove extract-derived AgNPs prepared under various conditions. Fourier-transform infrared (FTIR) spectroscopy analysis provided information about the surface interaction of the clove extract with the AgNPs. Ultrahigh-resolution transmission electron microscopy (UHRTEM) results confirmed the formation of spherical, uniformly distributed clove extract-capped AgNPs with sizes in the range of 2–20 nm (average size: 14.4 ± 2 nm). Powder X-ray diffractometry analysis (PXRD) illustrated the formation of pure crystalline AgNPs. These AgNPs were tested as a colorimetric sensor to detect trace amounts of vinclozolin (VIN) by UV-Vis spectroscopy for the first time. The AgNP-based sensor demonstrated very sensitive and selective colorimetric detection of VIN, in the range of 2–16 µM (R² = 0.997). The developed sensor was green, simple, sensitive, selective, economical, and novel, and could detect trace amounts of VIN with limit of detection (LOD) = 21 nM. Importantly, the sensor was successfully employed for the determination of VIN in real water samples collected from various areas in Turkey.

A visual and sensitive Hg2+ detection strategy based on split DNAzyme amplification and peroxidase-like activity of hemin-graphene composites

A visual and sensitive Hg²⁺ detection strategy was developed based on split DNAzyme amplification and hemin-graphene oxide composites (H-GNs). Two split DNAzyme sequences can form two entire enzyme-strands DNA (E-DNA) by T-Hg²⁺-T interaction. The E-DNA can bind with the loop of molecular beacon (MB) to form Mg²⁺-dependent DNAzyme structure. The formed DNAzyme can circularly cleave the loop of MB, resulting large amount of DNA fragments. The resultant DNA fragments can prevent H-GNs from aggregation by adsorbing on its surface. Consequently, the supernate with large amount of H-GNs shows dark blue color after chromogenic reaction. This strategy shows a linear range from 50 pM to 1200 pM. The limit detection can be low to 33 pM. This strategy provides a visual and enzyme-free amplification mode for quick and sensitive screen of Hg²⁺.

A hydrazono-quinoline-based chemosensor sensing In3+ and Zn2+via fluorescence turn-on and ClO−via color change in aqueous solution

A multi-target sensor, based on hydrazono-quinoline, was developed for fluorescence turn-on detection of In³⁺ and Zn²⁺ and colorimetric detection of ClO⁻.

A highly selective fluorescence sensing platform for nanomolar Hg(II) detection based on cytosine derived quantum dot

Inspired by low toxicity and good biocompatibility of biomass derived quantum dot (QD), we herein developed a cytosine derived quantum dot, namely cyt-dot, via a one-step hydrothermal synthesis. The as-prepared cyt-dot emits blue fluorescence (FL) containing abundant oxygen (20.6at.%) and nitrogen (24.1at.%) contents. The cyt-dot based sensing platform shows exclusive selectivity for Hg(II) while being insensitive towards Fe(III) and Ag(I), which are important interference that usually cannot be ruled out. The detection limit for Hg(II) is of 11nM, which is very close to the guideline value of 10nM allowed by the U.S. Environmental Protection Agency in drinking water. In real water sample analyses, the present sensing platform can fulfil satisfied recoveries ranging from 100% to 108%. Besides, the acidity of solution has almost no effect on the sensing performance of the cyt-dot in a pH range of 5-8, suggesting its potential applications in sensing and bio-imaging.

Thiamine-functionalized silver nanoparticles for the highly selective and sensitive colorimetric detection of Hg2+ ions

Hg²⁺ contamination is a serious threat to the environment; hence, the development of methods for its trace level detection is urgently required.

Applications of vitamin B6 cofactor pyridoxal 5'-phosphate and pyridoxal 5'-phosphate crowned gold nanoparticles for optical sensing of metal ions

Vitamin B6 cofactor pyridoxal 5'-phosphate (PLP) and PLP crowned gold nanoparticles (PLP-AuNPs) was applied for the optical chemosensing of metal ions in aqueous medium. PLP showed a visually detectable colour change from colourless to yellow and 'turn-off' fluorescence in the presence of Fe³⁺. The fluorescence intensity of PLP at 433nm was also blue-shifted and enhanced at 395nm upon addition of Al³⁺. When the PLP was functionalized over AuNPs surface, the wine red colour of PLP-AuNPs was turned to purplish-blue and the SPR band at ~525nm was red-shifted upon addition of Al³⁺, Cd²⁺ and Pb²⁺ due to the complexation-induced aggregation of nanoparticles. The developed sensing systems exhibited good selectivity and specificity for the detected analytes (Fe³⁺, Al³⁺, Cd²⁺ and Pb²⁺).

N-lauryltyramine capped copper nanoparticles exhibit a selective colorimetric response towards hazardous mercury(ii) ions and display true anti-biofilm and efflux pump inhibitory effects in E. coli

Hg²⁺ ions selectively decolorize CuNPs through aggregation.

Cefuroxime derived copper nanoparticles and their application as a colorimetric sensor for trace level detection of picric acid

Picric acid is used as explosive material in destructive weapons and nuclear technology. Due to higher solubility in water it can create health issues and its monitoring is crucial for safer environment and health.

Gold nanoparticle-based nanosystems for the colorimetric detection of Hg2+ ion contamination in the environment

This review highlights the impact of Hg²⁺ contamination on the human population and the need for its detection.

Barbituric acid–triphenylamine adduct as an AIEE-type molecule and optical probe for mercury(ii)

A barbituric acid–triphenylamine adduct displayed interesting aggregation-induced emission enhancement (AIEE) features in a THF–water co-solvent system and can act as a fluorescence turn-on probe for Hg²⁺.

Colorimetric detection of mercury species based on functionalized gold nanoparticles

The speciation analysis of heavy metal pollutants is very important because different species induce different toxicological effects. Nanomaterial-assisted optical sensors have achieved rapid developments, displaying wide applications to heavy metal ions but few to metal speciation analysis. In this work, a novel colorimetric nanosensor strategy for mercury speciation was proposed for the first time, based on the analyte-induced aggregation of gold nanoparticles (Au NPs) with the assistance of a thiol-containing ligand of diethyldithiocarbamate (DDTC). Upon the addition of mercury species, because Hg-DDTC was more stable than Cu-DDTC, a place-displacement between Hg species and Cu(2+) would occur, and thereby the functionalized Au NPs would aggregate, resulting in a color change. Moreover, by virtue of the masking effect of ethylenediaminetetraacetic acid (EDTA), the nanosensor could readily discriminate organic mercury and inorganic mercury (Hg(2+)), and it is thus anticipated to shed some light on the colorimetric sensing of organic mercury. So, a direct, simple colorimetric assay for selective determination of Hg species was obtained, presenting high detectability, such as up to 10 nM for Hg(2+) and 15 nM for methylmercury. Meanwhile, the strategy offered excellent selectivity toward mercury species against other metal ions. The simple, rapid, and sensitive label-free colorimetric sensor for the determination of Hg species provided an attractive alternative to conventional methods, which usually involve sophisticated instruments, complicated processes, and long periods of time. More importantly, by using mercury as a model, an excellent nanomaterial-based optical sensing platform can be developed for speciation analysis of trace heavy metals, which can lead to nanomaterials stability change through smart functionalization and reasonable interactions.

Optical reading of contaminants in aqueous media based on gold nanoparticles

With increasing trends of global population growth, urbanization, pollution over-exploitation, and climate change, the safe water supply has become a global issue and is threatening our society in terms of sustainable development. Therefore, there is a growing need for a water-monitoring platform with the capability of rapidness, specificity, low-cost, and robustness. This review summarizes the recent developments in the design and application of gold nanoparticles (AuNPs) based optical assays to detect contaminants in aqueous media with a high performance. First, a brief discussion on the correlation between the optical reading strategy and the optical properties of AuNPs is presented. Then, we summarize the principle behind AuNP-based optical assays to detect different contaminants, such as toxic metal ion, anion, and pesticides, according to different optical reading strategies: colorimetry, scattering, and fluorescence. Finally, the comparison of these assays and the outlook of AuNP-based optical detection are discussed.

Ultrasensitive, rapid, and selective detection of mercury using graphene assisted laser desorption/ionization mass spectrometry

We report an extremely sensitive and specific detection of mercuric ions (Hg²⁺) based on graphene assisted laser desorption/ionization mass spectrometry (GALDI-MS). Combining the highly selective coordination interactions between thymine (T) and Hg²⁺, we present a simple, effective, and novel approach, based on π-π interactions of the T-Hg²⁺-T complex and G that can serve as a platform and matrix for GALDI-MS. The present sensor not only exhibits high selectivity and sensitivity (picomolar) to Hg²⁺ in aqueous solution, but also can elucidate the chemical structures of the metal complexes. The significant advantage in the current approach is that there is no need for a sophisticated instrument, and no sample pretreatment is required to detect the Hg²⁺ ions.

Ultrasensitive surface-enhanced Raman scattering nanosensor for mercury ion detection based on functionalized silver nanoparticles

A SERS strategy for ultrasensitive detection of Hg²⁺ based on 4-mercaptopyridine functionalized AgNPs in the presence of spermine.

Colorimetric detection of mercury ions based on plasmonic nanoparticles

The development of rapid, specific, cost-effective, and robust tools in monitoring Hg(2+) levels in both environmental and biological samples is of utmost importance due to the severe mercury toxicity to humans. A number of techniques exist, but the colorimetric assay, which is reviewed herein, is shown to be a possible tool in monitoring the level of mercury. These assays allow transforming target sensing events into color changes, which have applicable potential for in-the-field application through naked-eye detection. Specifically, plasmonic nanoparticle-based colorimetric assay exhibits a much better propensity for identifying various targets in terms of sensitivity, solubility, and stability compared to commonly used organic chromophores. In this review, recent progress in the development of gold nanoparticle-based colorimetric assays for Hg(2+) is summarized, with a particular emphasis on examples of functionalized gold nanoparticle systems with oligonucleotides, oligopeptides, and functional molecules. Besides highlighting the current design principle for plasmonic nanoparticle-based colorimetric probes, the discussions on challenges and the prospect of next-generation probes for in-the-field applications are also presented.

Highly sensitive and selective colorimetric sensing of Hg2+ based on the morphology transition of silver nanoprisms

A simple colorimetric approach for mercury ion (Hg(2+)) sensing was developed that was based on the Hg(2+)-induced deprotection and morphology transition of 1-dodecanethiol (C(12)H(25)SH)-capped silver nanoprisms (Ag NPRs) upon the presence of iodides at room temperature. The abstraction of C(12)H(25)SH from the surface of Ag NPRs by Hg(2+) led to their deprotection of Ag NPRs and the formation of complexation between silver ions and excess iodide ions. Also, the silver atoms were consumed and moved from the surface of Ag NPRs, accompanying the changes in the particle morphology that resulted in a change of color and UV-vis absorption spectra of the colloidal solution. With increasing concentrations of Hg(2+) from 10 to 500 nM, the surface plasma resonance spectral band of Ag NPRs emerged as a blue shift and exhibited a good linear relationship, and the limit of detection was 3.3 nM. Furthermore, the developed method was applied for detecting Hg(2+) in different real water samples with satisfying recoveries over 92%.

Detection of mercury ions based on mercury-induced switching of enzyme-like activity of platinum/gold nanoparticles

In this study, bimetallic platinum/gold nanoparticles (Pt/Au NPs) were found to exhibit peroxidase-like activity, and the deposition of mercury was found to switch the enzymatic activity to a catalase-like activity. Based on this phenomenon, we developed a new method for detecting mercury ions through their deposition on bimetallic Pt/Au NPs to switch the catalytic activity of Pt/Au NPs. Pt/Au NPs could be easily prepared through reduction of Au(3+) and Pt(4+) by sodium citrate in a one-pot synthesis. The peroxidase catalytic activity of the Pt/Au NPs was controlled by varying the ratios of Pt to Au. The Pt(0.1)/Au NPs (prepared with a [Au(3+)]/[Pt(4+)] molar ratio of 9.0/1.0) showed excellent oxidation catalysis for H(2)O(2)-mediated oxidation of Amplex® Red (AR) to resorufin. The oxidized product of AR, resorufin, fluoresces more strongly (excitation/emission wavelength maxima ca. 570/585 nm) than AR alone. The peroxidase catalytic activity of Pt(0.1)/Au NPs was switched to catalase-like activity in the presence of mercury ions in a 5.0 mM tris(hydroxymethyl)aminomethane (Tris)-borate solution (pH 7.0) through the deposition of Hg on the particle surfaces owing to the strong Hg-Au metallic bond. The catalytic activity of Hg-Pt(0.1)/Au NPs is superior (by at least 5-fold) to that of natural catalase (from bovine liver). Under optimal solution conditions [5.0 mM Tris-borate (pH 7.0), H(2)O(2) (50 mM), and AR (10 μM)] and in the presence of the masking agents polyacrylic acid and tellurium nanowires, the Pt(0.1)/Au NPs allowed the selective detection of inorganic mercury (Hg(2+)) and methylmercury ions (MeHg(+)) at concentrations as low as several nanomolar. This simple, fast, and cost-effective system enabled selective determination of the spiked concentrations of Hg(2+) and MeHg(+) in tap, pond, and stream waters.

Novel Hg2+-imprinted polymers based on thymine-Hg2+-thymine interaction for highly selective preconcentration of Hg2+ in water samples

A novel functional monomer T-IPTS, 3-isocyanatopropyltriethoxysilane (IPTS) bearing thymine (T) bases, was synthesized for imprinting Hg(2+). Then a novel Hg(2+) ionic imprinted polymers (IIPs) based on thymine-Hg(2+)-thymine (T-Hg(2+)-T) interactions, i.e. Hg-IIPs-T, were prepared by sol-gel process for the first time in this work. The Hg-IIPs-T exhibited excellent selectivity towards Hg(2+) over Cd(2+), Zn(2+) Pb(2+), Co(2+), Mn(2+), Mg(2+) and Ca(2+), due to the specific T-Hg(2+)-T interactions with high selectivity and high affinity. Accordingly, Hg-IIPs-T were used as solid-phase extraction (SPE) sorbents for preconcentration of trace Hg(2+) in water samples, and satisfactory recoveries ranging from 95.2 to 116.3% were obtained. Also, under optimized conditions, preconcentration factor and detection limit were achieved of 200 and 0.03 μg L(-1), respectively. The IIPs-T-SPE proved to be a rapid and high-effective cleanup and enrichment method for trace Hg(2+) in water samples. More importantly, these results indicated that devising and synthesizing new functional monomers tailor-made for template would become a general promising way to improve the selectivity and stability of IIPs.