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The use of nanomaterials and nanotechnology to construct a smart pesticide delivery system with target-oriented and controlled-release functions is important to increase the effective utilization rate and minimize environmental residue pollution. A temperature-dependent delivery system can modulate the release of pesticide with temperature to improve the efficacy and precision targeting. A series of poly(

Fungicide-resistant Fusarium has become a threaten to wheat production. Novel fungicide formulations can improve the efficacy of active ingredient and minimize the emergence of resistance. Encapsulation of fungicides in biodegradable carriers, especially, in polysaccharide, is a feasible approach to develop environment-friendly and efficient formulation. This study focused on the synthesis of ethyl cellulose-based phenamacril nano-delivery system by combining emulsion-solvent evaporation and high-pressure homogenization technology to improve the control of fusarium head blight in wheat. Emulsifier 125 and Tersperse 2500 were screened from eleven commonly used surfactants. Emulsifier 125 and Tersperse 2500 in a ratio of 2:1 and phenamacril nanocapsules with the mean particle size of 152.5 ± 1.3 nm were prepared. These showed excellent storage stability and wettability on crop leaves. A bioassay comparing the nanocapsules with a commercial preparation against Fusarium graminearum showed significantly improved biological activity. This formulation could be used to effectively not only to control fusarium head blight but also delay the occurrence of resistance.

Pesticide compounding technology for disease and pest control emerges as an effective way to increase the effectiveness of pesticides while reducing pesticides resistance. Nanomaterials and encapsulation technology have offered a new insight into preparing efficient pesticide formulations, especially constructing a co-delivery nanoparticle for synergistic pesticides. In this study, a dinotefuran/avermectin co-delivery nanoparticles (DACNPs) against pear tree pests with polylactic acid (PLA) as the wall material were constructed by double-emulsion method combined with high-pressure homogenization technique. The drug content of the DACNPs was 39.1% with an average size of 245.7 ± 4.2 nm and the mean polymer dispersity index (PDI) value was 0.123. The DACNPs showed high foliar retention and good spread performance on target leaves due to the nanoscale effect. The obtained DACNPs showed a better control effect on Grapholitha molesta Busck and Psylla chinensis Yang et Li compared with the commercial formulations, which could significantly prolong the effective duration and enhance the bioactivity with lower amounts and application frequency of pesticides. This study may provide new insights into developing novel pesticide formulations to improve the utilization rate of pesticides, reduce environmental pollution and minimize the cost of farming.

A 1-triacontanol modified layered double hydroxide (tria-LDH) is prepared via a self-assembly method. It can achieve sustainable growth regulation to alleviate drought stress through the promotion of the SOD activity, which is confirmed by the reduced accumulation of MDA.

A pH/enzyme dual-responsive zein-EMB-nanocapsule system was prepared via a phase-separation method, which could enhance the pesticide's adhesion, target wettability, stability, anti-photolysis, and stimuli-responsive controlled release properties.

Pesticides are commonly used in modern agriculture and are important for global food security. However, postapplication losses due to degradation, photolysis, evaporation, leaching, surface runoff, and other processes may substantially reduce their efficacy. Controlled-release formulations can achieve the permeation-regulated transfer of an active ingredient from a reservoir to a target surface. Thus, they can maintain an active ingredient at a predetermined concentration for a specified period. This can reduce degradation and dissipation and other losses and has the potential to improve efficacy. Recent developments in controlled-release technology have adapted the concepts of intelligence and precision from the pharmaceutical industry. In this review, we present recent advances in the development of controlled-release formulations and discuss details of the preparation methods, material improvements, and application technologies.

Lipopolysaccharide (LPS) poses a considerable threat to food safety and human health. A colorimetric assay for LPS detection based on LPS binding aptamer (LBA) and SYBR Green I (SG) mediated aggregation of gold nanoparticles (AuNPs) was established. In the absence of LPS, the LBA was absorbed onto the AuNPs surface which prevented SG-induced aggregation of AuNPs, and the sensing system exhibited red color. When LPS was added, it interacted with the LBA, forming a complex. At higher LPS concentration, many LBAs were exhausted resulting in SG-induced aggregation of AuNPs, and color change from red to blue. The range of colorimetric detection of LPS was linear in 0-12 EU/mL, with a limit of detection of 0.1698 EU/mL. Spiked LPS in real samples and interfering substances were also identified. This assay ingeniously using the fluorescent dye SG as an effective trigger of AuNPs aggregation, is rapid and facile than most of those earlier reported LBA-based LPS assays, and there is potential to be modified to construct assays for other targets.

Emamectin benzoate (EMB), a frequently used biopesticide, is poorly soluble in water, making it difficult to wet the leaf surface, is prone to degrade in sunlight and readily loses its bioactivity. Traditional methods such as organic solvent application, pH adjustment and addition of photoprotectants either increase the economic and environmental costs or barely achieve the desired goal. We hypothesized that nanotechnology could improve the solubility, foliar affinity, photostability and bioactivity of EMB. This research set out to prepare a nano-EMB solid powder (nano-EMB-SP) and test this hypothesis.Nano-EMB-SP was prepared using a self-emulsifying method combined with carrier solidification. The mean particle size and Polydispersity index (PDI) of nano-EMB-SP were 14.64 nm and 0.24, respectively. A scanning electron microscopy image showed that EMB nanoparticles were mainly spherical or ellipsoidal in shape. Without organic solvent, the aqueous solubility of EMB in nano-EMB-SP was 4500 mg LNano-EMB-SP is an eco-friendly and efficient way to improve the solubility, foliar affinity, photostability and bioactivity of EMB. This research provides a good approach to improving the efficacy of poorly soluble and UV-sensitive pesticides. © 2022 Society of Chemical Industry.

Telomerase and microRNAs (miRNAs) as important biomarkers are closely related to cancers. Simultaneous detection of telomerase activity and miRNAs would be beneficial to improve the specificity and reliability. Here, we establish a telomerase and miRNA-21 (miR-21) simultaneous sensing platform with graphene oxide-based fluorescent aptasensors (GOFA) including graphene oxide (GO), template strand (TS) primer and fluorophore-labeled telomerase/miR-21 oligonucleotides. Owing to π-π stacking interaction, TS primer and telomerase/miR-21 probes would be loaded onto GO, resulting in fluorescence quenching. However, in the presence of the telomerase or miR-21, the double-stranded oligonucleotides would be away from the GO surface attribute to the hybridization between the extended TS primers and telomerase probe as well as miR-21 and miR-21 probe, leading to obvious fluorescence recovery. We found that GOFA could simultaneously detect telomerase activity and miR-21 with low background signal, high sensitivity and simplified operation. Moreover, GOFA could be used for accurately detecting telomerase activity and miRNA in living cells and cancer patient tissue sample. This sensing platform shows great potential in improving the accuracy in clinical diagnosis of cancer.

ZIF-8(zinc-methylimidazolate framework-8), one of the zeolitic imidazolate frameworks (ZIFs), was put into a tea bag for selective removal of oils from water surface, and exhibits strong hydrophobicity with a water contact angle of 142°, ZIF-8 particles combined with highly hydrophobic and superoleophilic properties. Our Experiment results showed that the highly hydrophobic ZIF-8 particles and the ZIF-8/tea bag could be reused in oil-water separation for twenty cycles. More importantly, the oil could be readily removed from the surfaces of particles by heating combined with reduced pressure treatment whereas the particles still kept highly hydrophobic and superolephilic characteristics, which render its potential applications in the cleanup of oil spills and the removal of organic pollutants on water surface.

Special wettable surfaces (SWS, i.e., surfaces with special wettability) are less common in daily life. Some of the frequently studied SWS include those surfaces of homogeneous wettability which are superhydrophobic, superoleophobic, or omniphobic. Additionally, surfaces of patterned wettability which are partially hydrophilic and partially hydrophobic have also been widely investigated. Besides their wide applications in self-cleaning, anti-fogging, water-harvesting, anti-icing, water-oil separation and anticorrosion, the SWS have also been emergingly utilized in biological and chemical sensing in recent years. This review focuses on the SWS-based sensing applications, and classified them into electrical/electrochemical assays, surface-enhanced Raman scattering (SERS) assays, fluorescent/colorimetric assays, and visual assays (i.e. assays based on contact angle). After the main characteristics and performances of these applications were briefly summarized, areas to be improved and direction for future development of this research topic were discussed at the end of the review.

Graphical abstract As one kind of noble metal nanostructures, the plasmonic gold nanostructures possess unique optical properties as well as good biocompatibility, satisfactory stability, and multiplex functionality. These distinctive advantages make the plasmonic gold nanostructures an ideal medium in developing methods for biosensing and bioimaging. In this review, the optical properties of the plasmonic gold nanostructures were firstly introduced, and then biosensing in vitro based on localized surface plasmon resonance, Rayleigh scattering, surface-enhanced fluorescence, and Raman scattering were summarized. Subsequently, application of the plasmonic gold nanostructures for in vivo bioimaging based on scattering, photothermal, and photoacoustic techniques has been also briefly covered. At last, conclusions of the selected examples are presented and an outlook of this research topic is given.

The capability to image, as well as control and manipulate single molecules such as nucleic acids (DNA or RNA) can greatly enrich our knowledge of the roles of individual biomolecules in cellular processes and their behavior in native environments. Here we summarize the recent advances of single nucleic acid imaging based on optical observation and force manipulation. We start by discussing the superiority of single molecule image, the central roles nucleic acids play in biosystems, and the significance of single molecule image towards nucleic acids. We then list a series of representative examples in brief to illustrate how nucleic acid of various morphologies has been imaged from different aspects, and what can be learned from such characterizations. Finally, concluding remarks on parts of which should be improved and outlook are outlined.

This paper reports a new assay platform that performed in polar organic solutions for ultrasensitive and highly selective detection of isocarbophos pesticide. The sensing system just contains hemin molecules and random ssDNAs. Free hemin molecules have a strong absorption peak at Soret band in polar organic solvents, and they can assemble into few small particles with random ssDNAs via their special π–π stacking interaction. However, the subsequent addition of isocarbophos into above sensing system can aggregate hemin molecules to form many larger particles, which result in a great decrease in absorbance value of sensing solution. UV/Vis absorption spectra and scanning probe microscope (SPM) were used to characterize hemin aggregation. Additionally, the effects of some parameters like type of solvents, hemin amount and random ssDNAs on the sensing platform were also investigated. The present assay platform has a detection limit as low as 0.2 μg/L, a dynamic range of 0.5–500 μg/L, and high selectivity over other competitive pesticides. Moreover, the assay platform also displays excellent stability and accuracy in the detection of spiked real samples, suggesting that such sensing platform will play an important role in biological and environmental detection.

The authors describe an aptasensor for the detection of the gonadal hormone progesterone (P4) in aqueous solution. Gold nanoparticles (AuNPs) were coated with a P4-specific aptamer, and such particles do not aggregate in presence of NaCl due to the presence of the aptamer coating. If, however, progesterone is added, it will bind to the aptamer and release it from the surface. The uncoated AuNPs, on addition of NaCl, will aggregate and a color change from red (520 nm) to blue (650 nm) can be visually detected or photometrically quantified. The ratio of the absorbances at 650 and 520 nm is linearly related to the P4 concentration in the range from 2.6 to 800 nM. The complete detection range extends from 2.6 to 1400 nM, and the detection limit is 2.6 nM. Water containing various potential interferents, as well as tap water and urine, were spiked with P4 and the recoveries of P4 are in the range of 89.7–117.5%, 84.4–115.0% and 94.7–118.8%, respectively. This assay has a large potential with respect to the visual and instrumental determination of P4 in aquatic environment and urine.

In this study, a colorimetric method was exploited to detect bisphenol A (BPA) based on BPA-specific aptamer and cationic polymer-induced aggregation of gold nanoparticles (AuNPs). The principle of this assay is very classical. The aggregation of AuNPs was induced by the concentration of cationic polymer, which is controlled by specific recognition of aptamer with BPA and the reaction of aptamer and cationic polymer forming "duplex" structure. This method enables colorimetric detection of BPA with selectivity and a detection limit of 1.50 nM. In addition, this colorimetric method was successfully used to determine spiked BPA in tap water and river water samples.

The authors describe a label-free electrochemical aptasensor for tetracycline (TET). The TET-binding aptamer was immobilized on a composite consisting of reduced graphene oxide, magnetite (Fe3O4) and sodium alginate, and this material was used to modify the surface of a screen-printed carbon electrode (SPCE). Cyclic voltammetry was carried out to characterize the single steps in the preparation of the modified electrode and to optimize the conditions for detection. Differential pulse voltammetry (DPV) was then used to monitor the interaction between aptamer and TET by applying the electrochemical probe thionine. Under optimal conditions, TET can be quantified by DPV in the 1 nM to 5 μM concentration range, with a detection limit as low as 0.6 nM (at an S/N ratio of 3). The method is rapid, cost-efficient, highly sensitive and specific, and therefore is considered to be a viable platform for TET analysis in food, environmental, and clinical samples.

Polyethylene glycol (PEG) was introduced into carboxymethyl cellulose (CMC) to form hydrophilic chain of PEG-CMC. Avermectin (Avm) was grafted on the long chain of PEG-CMC by use of N, N-dicyclohexylcarbodiimide (DCC) as the dehydrant and 4-dimethylaminopyridine (DMAP) as the catalyst to form the amphiphilic molecule. Then the avermectin nanoparticles was prepared with esterase-responsive sustained release successfully through self-assembly. The size of nanoparticles was less than 400 nm. Avermectin loading was 8% and the degradation rate was less than 50 % under the xenon arc lamp for 72 h. Compared with avermectin technical, it showed an obvious anti-photodegradation advantage. Compared with commercially available water-dispersible granules (WDG), the avermectin nanoparticles had a smaller contact angle on the cucumber leaf surface and there was a significant difference. The toxicity test showed that the nanoparticles have a certain insecticidal effect on the larva of Hyphantria cunea and the sensitivity increased gradually over time.

Among the methods developed for protein sandwich assays, the strategies based on fluorescence, electrochemistry, and color change occupy the predominant portion. However, besides these three major types, there are some other techniques, such as use of surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS), giant magnetoresistive (GMR), quartz crystal microbalance (QCM), microcantilever, surface acoustic wave (SAW), and resonance Rayleigh scattering (RRS), which also play a very important role in the development of the sandwich assay for protein detection. Through integrating different recognition molecules, such as antibodies and aptamers, with conventional or new immerging sensing platforms, these assays exhibit excellent comparable sensitivities and specificities and attract extensive attention. Thus, in this chapter, some recent advances in these fields are summarized and concluding remarks on parts of which should be improved as well as outlook are outlined.

ZIF-8(zinc-methylimidazolate framework-8), one of the zeolitic imidazolate frameworks (ZIFs), as quenching platforms for detection of HIV-1 DNA, which was identified to be effective for highly sensitive detection of HIV-1 DNA. The enhanced fluorescence signal has a relationship with the ssDNA concentration, the detection limit is as low as 1.2 nmol L-1 with good selectivity. This study is an important step toward rational design of materials to achieve specific interactions between biomolecules and synthetic particle surfaces.

We report on an “off-on” type of fluorescent assay for silver(I) ion determination that is based on the use of silver-specific DNA, gold nanoparticles, and Rhodamine B (RhoB). The random coil cytosine-rich silver-specific DNA undergoes structural transformation on capturing Ag(I), and this results in a change in the aggregation status of the gold nanoparticles and simultaneously affects the fluorescence intensity of RhoB that was added to the solution. The fluorescence intensity of RhoB is related to the concentration of Ag(I) in the 2.73 to 1500 ppb range, and the detection limit is 2.73 ppb. The method was applied to the determination of Ag(I) in (spiked) water samples. Conceivably, it also may be applied to fluorescence imaging silver ions and, by using other ion-specific DNAs, to detect other metal ions.

A label-free fluorescent DNA-based sensor for the detection of Pb2+ and Hg2+ has been reported in this paper. A single-stranded DNA named modified T30695 was used as a recognition probe and SYBR Green I (SG) was used as a signal reporter. This sensor consisted of two interaction sections: Pb2+ interacts with modified T30695 to form a G-quadruplex and Hg2+ interacts with modified T30695 to form a T–Hg(II)–T hairpin conformation. Circular dichroism confirmed the interactions between modified T30695 and Pb2+ or Hg2+. Based on this, a sensor for the detection of Pb2+ and Hg2+ with limits of detection of 2.09 ppb and 1.14 ppb was constructed.

We report a rapid, visual, facile colorimetric detection of melamine in raw milk by unmodified gold nanoparticles (AuNPs). AuNPs can be induced by melamine from dispersion to aggregation rapidly, along with the color change from red to blue (or purple). After the optimization of reaction conditions, the whole analysis only needs about 20 min including the simple pretreatment we designed. The analysis can be observed by the naked eye and simple to operate without sophisticated instruments. In the raw milk, the present limit of detection for melamine is down to ∼70 ppb. Furthermore, we explore the interaction principle between melamine and citrate-stabilized AuNPs in this work and establish the foundation for modifying the AuNPs and optimizing the system of AuNPs–melamine in the future.

Recent years have witnessed great progress in developing functional nucleic acids (FNAs)-based sensors for the detection of heavy metal ion. In this review, four types of the FNAs that most widely-used in heavy metal ions detection were briefly introduced and a dozen of recently published review articles which summarized those FNAs-based sensors were introduced. Particularly, according to the degree of automation and system integration, those FNAs-based sensors which belong to the lab-on-a-chip (LOC) category were reviewed in more detail by classifying them into six types such as microfluidic LOC system, microchip, lateral flow dipstick, personal glucose meter, microfluidic paper-based analytical devices (μPADs) and disc-based analytical platform. After gave a brief description of the sensing strategies, properties, advantages or disadvantages of these FNAs-based sensors, existing problems and future perspectives were also discussed.

This paper reports a simple fluorescent assay for the determination of Hg(2+) and Pb(2+) by using a DNA intercalator GeneFinder™ (GF) and an integrated functional nucleic acid (FNA). In the absence of Hg(2+) and Pb(2+), GF intercalated with the FNA and released moderate strong fluorescence. While in the presence of Hg(2+) or Pb(2+), the FNA would be induced to form T-Hg(2+)-T or G-quadruplex structure, interacted with which the GF would exhibit extremely strong or very weak fluorescence. By monitoring the fluorescence changes upon addition of these two ions, the Hg(2+) and Pb(2+) could be selectively detected as low as 3.23 ppb and 2.62 ppb. As the main advantage of this assay is simplicity and the feasibility was demonstrated by detecting Hg(2+) and Pb(2+) in spiked water samples, this assay holds great potential for the development of a cost effective and useful tool for environmental monitoring.

This paper reports a fluorescent turn-off assay for sensitive detection of Cu(2+) in an aqueous solution by using a copper-specific ssDNA Cu100 and Sybr Green I. By monitoring the fluorescence changes arose from different interactions of Sybr Green I with Cu100 and Cu100/Cu(2+) complex, the Cu(2+) could be linearly detected from 5.57 to 250 ppb, with a detection limit of 5.57 ppb. The feasibility of this assay was demonstrated by detecting Cu(2+) in certified reference materials and spiked water samples with satisfactory results.

The demand for selection of aptamers against various small chemical molecules has substantially increased in recent years. To incubate and separate target-specific aptamers, the conventional SELEX procedures generally need to immobilize target molecules on a matrix, which may be impotent to screen aptamers toward small molecules without enough sites for immobilization. Herein we chose Cd(II) as a model of a small molecule with less sites, and proposed a novel SELEX strategy of immobilizing ssDNA libraries rather than target molecules on a matrix, for selection of aptamers with high affinity to Cd(II). After eleven rounds of positive and negative selection, twelve T and G-rich of nonrepeating ssDNA sequences were identified, of which the Cd-4 aptamer displayed the highest binding affinity to Cd(II). The secondary structures of these sequences revealed that a stem-loop structure folded by the domain of their 30-random sequence is critical for aptamers to bind targets. Then the interaction between the selected Cd-4 aptamer and Cd(II) was confirmed by CD analysis, and the binding specificity toward other competitive metal ions was also investigated. The dissociation constant (Kd) of Cd-4 aptamer was determined as 34.5 nM for Cd(II). Moreover, the Cd-4 aptamer was considered a recognition element for the colorimetric detection of Cd(II) based on the aggregation of AuNPs by cationic polymer. Through spectroscopic quantitative analysis, Cd(II) in aqueous solution can be detected as low as 4.6 nM. The selected Cd-4 aptamer will offer a new substitute for the detection of Cd(II) or other applications like recovery of cadmium from polluted samples.

This paper reports an ultrasensitive resonance scattering (RS) method to detect tetracycline (TET) in milk based on the competition of aptamers between nanogold and TET, aggregation of naked nanogold, nanocatalytic Fehling reaction, and RS signals of catalytic product Cu2O cubic. The detection principle was confirmed by the nanoparticle size analyzer (NANOS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The variations of RS intensity had good linear correlation with TET concentrations, and the limit of detection was calculated as 11.6 nM. The proposed method was successfully applied for analysis of TET in milk, with total recoveries ranging from 105 to 109%.

Concern is mounting regarding the human health and environment effects of 17β-estradiol (E2), a natural oestrogen excreted by human beings and animals. In this paper, a sensitive and selective biosensor for the detection of E2 using gold nanoparticles (AuNPs), label-free E2-specific aptamer, and poly(diallyldimethylammonium chloride) (PDDA) was developed. In the absence of E2, PDDA can electrostatically interact with E2-specific aptamer, and the charge responsible for inducing AuNPs aggregation was destroyed. However, the introduction of E2 can specifically interact with the aptamer to form E2–aptamer complex so that PDDA can aggregate AuNPs and cause a remarkable change in colour from wine red to blue, which enables colorimetric detection of E2 with selectivity and a detection limit of 1.57 nM.

As(III) specifically interacts with an arsenic-binding aptamer to form an As(III)–aptamer complex, so that the following cationic polymer can aggregate gold nanoparticles (AuNPs) and cause a remarkable change in color, which enables the colorimetric detection of As(III) with high selectivity and a detection limit of 5.3 ppb.

Deoiled Jatropha curcas seed meal (DJSM), a chief waste material of oil extraction industry, will be generated on a large scale due to the growing interest in using Jatropha curcas seed oil as a feedstock for the production of biodiesel. Up to now, there is very little work on viable approach for the use of DJSM to the best of our knowledge. This article reports our studies on the utilization of this huge biomass by solid-state fermentation (SSF) for the production of protease. Aspergillus niger was purchased and used for fermentation. The optimal fermentation conditions and the protease properties were studied. Maximum protease production (9204U/g of dry substrate, U/g) was obtained at 50% of substrate moisture, a growth period of 4 days, supplementation with 5% (wt) of glucose. The results of protease characterization showed that the optimal temperature and pH were 50°C and 4.0, respectively. The Vmax and Km of the protease from Aspergillus niger were 0.0028 µmol (s mg)-1 protein and 0.1854 mM, respectively. Organic solvent can enhance enzyme activity. In comparison with control, the activities were increased by 31.21% and 24.11% when the protease was solved by 15% (v/v) of methanol and 10% (v/v) of ethanol, respectively.

The catalytic activity of higher concentration of hemin can be temporarily inhibited by arsenic-binding aptamers, and it will recover in the presence of As(III) due to the exhaustion of aptamers, so the subsequent TMB molecules can be oxidized thoroughly and cause a remarkable increase of absorbance value at 442 nm, which enables the colorimetric detection of As(III) with high selectivity and a detection limit of 6 ppb.

A fluorescence quenching result was obtained when an FAM-labelled G-rich oligonucleotide T30695 was treated with Pb2+, owing to the formation of a lead(II)-stabilized G-quadruplex. Based on this phenomenon a selective fluorescent assay for lead(II) detection with a limit of detection of 0.77 ppb and a detection range from 0 to 200 ppb was constructed.

We report a rapid and facile colorimetric sensing method for melamine detection in milk using aptamer based nanoparticles (AuNPs). Aptamers can absorb on the surface of AuNPs and electrostatically interact with poly(diallyldimethylammonium chloride) (PDDA), which protects the AuNPs from aggregation. The introduction of melamine causes a melamine–aptamer complex to form via hydrogen bonding, thus the resulting cationic polymer can aggregate the AuNPs and cause a remarkable change in color. As a result of this, the presence of melamine can be determined by the naked eye and by measuring absorbance. This sensor is selective for the detection of melamine in milk samples and has a limit of detection of 34 nM. Since aptamer-modified AuNPs are more stable and selective than unmodified AuNPs in the sensing of melamine, we hope that this type of detection method will be helpful for the detection of other small molecules.

This paper describes a simple and sensitive colorimetric sensor employing single-stranded DNA (ssDNA) ligand, cationic polymer, and gold nanoparticles (AuNPs) to detect silver ions. The positively charged polymer can electrostatically interact with ssDNA and destroy the charge balance leading to induction of AuNP aggregation. Silver ions (Ag+) can bind to cytosine (C)-rich nucleic acids to form the C-Ag+-C hair-pin structure, which can prevent its interaction with polymers. The resulting cationic polymer could aggregate AuNPs causing a remarkable change in colour. The concentration of Ag+ can be determined visually. This sensing platform exhibits high sensitivity and selectivity towards Ag+ versus other metal ions, with a detection limit of 48.6 nM. The assay did not require any labelling or modifying steps. This method is simple, effective, and convenient and can in principle be used to detect other metal ions or small molecules.

This paper reports the colorimetric and resonance scattering (RS)-based biosensor for the ultrasensitive detection of As(III) in aqueous solution via aggregating gold nanoparticles (AuNPs) by the special interactions between arsenic-binding aptamer, target and cationic surfactant. Aptamers and the cationic surfactant could assemble to form a supramolecule, which prevented AuNPs from aggregating due to the exhaustion of cationic surfactant. The introduction of As(III) specifically interacted with the arsenic-binding aptamer to form the aptamer-As(III) complex, so that the following cationic surfactant could aggregate AuNPs and cause the remarkable change in color and RS intensity. The results of circular dichroism (CD) and scanning probe microscope (SPM) testified to the formation of the supramolecule and aptamer-As(III) complex, and the observation of transmission electron microscope (TEM) further confirmed that the aggregation of AuNPs could be controlled by the interactions among the aptamer, As(III) and cationic surfactant. The variations of absorbance and RS intensity were exponentially related to the concentration of As(III) in the range from 1 to 1500 ppb, with the detection limit of 40 ppb for the naked eye, 0.6 ppb for colorimetric assay and 0.77 ppb for RS assay. Additionally, the speed of the present biosensor was rapid, and it also exhibited high selectivity over other metal ions with an excellent recovery for detection in real water samples, suggesting that the proposed biosensor will play an important role in environmental detection.

We report a label-free, silver-specific DNA-based bio-assay for the detection of silver ion (Ag+) in aqueous solution. The bio-assay relies on the structural change of cytosine (C)-rich silver-specific DNA and the status transition of gold nanoparticles (AuNPs). In the absence of Ag+, unfolded silver-specific DNA stabilizes the dispersed AuNPs at high salt concentrations, which induces low resonance Rayleigh scattering (RRS) intensity. However, in the presence of Ag+, silver-specific DNA folds into a hairpin conformation through C–Ag+–C mismatches, and cannot coat on the surface of AuNPs. Thus, the uncoated AuNPs aggregate at high salt concentrations and cause a significant increase in RRS intensity, which reflects the amount of Ag+ in the system. Under the optimized conditions, the RRS intensity at 550 nm increased linearly with the concentration of Ag+ ranging from 0.20 μM to 1.00 μM, and the limit of detection for Ag+ was determined as 0.202 μM. The bio-assay also shows high selectivity against coexisting cations.

A sensitive sensor for detection of daunomycin (DNR) was developed by using free-labeled gold nanoparticles (AuNPs) and DNR aptamer. In the absence of DNR, free aptamer could absorb onto the surface of AuNPs to prevent them from aggregating in high salt solution. In the presence of DNR, the aptamer was firstly exhausted due to the formation of a DNR/aptamer complex, which lead to the remarkable change of resonance scattering (RS) intensity at 550 nm. Such sensor showed high selectivity and a detection limit of 17.1 nM. Based on the advantage of the sensor, the proposed sensing method is believed to be implemented to the on-site and real-time DNR detection in food safety and other applications.