A Multicolor Immunosensor for Sensitive Visual Detection of Breast Cancer Biomarker Based on Sensitive NADH-Ascorbic-Acid-Mediated Growth of Gold Nanobipyramids

Simple dual-readout immunosensor based on phosphate-triggered and potassium permanganate for visual detection of fenitrothion

Multicolor-based visual immunosensor is a promising tool for rapid analysis without the use of bulky instruments. Herein, an anti-fenitrothion nanobody-alkaline phosphatase fusion protein (VHHjd8-ALP) was employed to develop a multicolor visual immunosensor (MVIS) and a ratiometric fluorescence MVIS (RFMVIS, respectively). After one-step competitive immunoassay, the VHHjd8-ALP bound to microplate catalyzed phenyl phosphate disodium salt (ArP) into phenol. Under high alkaline condition (pH 12), the phenol reduced KMnO4 to intermediate (K2MnO4) and further to MnO2 in alkaline condition (pH 12), accompanied by a visible color transition of purple-green-yellow, which can be used for semiquantitative visual analysis or qualitative detection by measuring RGB value. RFMVIS was proposed on the basis of MVIS to further improve sensitivity. The CdTe quantum dot and fluorescein were used as signal probes to develop the fluorescent immunosensor. The CdTe dots with red emission (644 nm) was quenched by oxidation of KMnO4, whereas the fluorescein with green emission (520 nm) remained constant, accompanied by a fluorescent color transition of green-yellow-red. By measuring the ratio of the fluorescence intensity (I644/I520), the ratiometric fluorescence immunosensor was developed for qualitative analysis. The two visual immunosensors were sensitive and simple, and they showed good accuracy and practicability in the recovery test, thus are ideal tools for rapid screening.

An ultrasensitive ratiometric electrochemical aptasensor based on metal-organic frameworks and nanoflower-like Bi2CuO4 for human epidermal growth factor receptor 2 detection

An ultra-sensitive ratiometric electrochemical aptasensor was constructed based on metal-organic frameworks (MOFs) and bimetallic oxides for the detection of the human epidermal growth factor receptor 2 (HER2), a breast cancer marker. The aluminum metal-organic framework (Al-MOF) and cerium-metal-organic framework (Ce-MOF) have higher specific surface area, which is conducive to load more aptamers or complementary DNA (cDNA), and realize the amplification of internal reference signal Fc. Furthermore, nanoflower-like bismuth copper oxide (Bi2CuO4) with abundant active sites was introduced to modify more aptamers on its surface, which were then fixed to the glassy carbon electrode (GCE) to amplify the detection signal. The quantitative detection of HER2 was achieved by differential pulse voltammetry (DPV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The materials were characterized by scanning electron microscope, transmission electron microscope, Zeta potential analyzer, X-ray diffraction and X-ray photoelectron spectroscopy. The ratiometric electrochemical aptasensor based on nanomaterial and chain displacement signal amplification technology could discern HER2 in a very wide range (0.001-20.0 ng/mL) with an extremely low detection limit (0.049 pg/mL) and has demonstrated good performance in clinical serum analysis. This strategy also provides a feasible idea for sensitive analysis of other clinical tumor markers.

Overview on the Development of Alkaline-Phosphatase-Linked Optical Immunoassays

The drive to achieve ultrasensitive target detection with exceptional efficiency and accuracy requires the advancement of immunoassays. Optical immunoassays have demonstrated significant potential in clinical diagnosis, food safety, environmental protection, and other fields. Through the innovative and feasible combination of enzyme catalysis and optical immunoassays, notable progress has been made in enhancing analytical performances. Among the kinds of reporter enzymes, alkaline phosphatase (ALP) stands out due to its high catalytic activity, elevated turnover number, and broad substrate specificity, rendering it an excellent candidate for the development of various immunoassays. This review provides a systematic evaluation of the advancements in optical immunoassays by employing ALP as the signal label, encompassing fluorescence, colorimetry, chemiluminescence, and surface-enhanced Raman scattering. Particular emphasis is placed on the fundamental signal amplification strategies employed in ALP-linked immunoassays. Furthermore, this work briefly discusses the proposed solutions and challenges that need to be addressed to further enhance the performances of ALP-linked immunoassays.

FeNC nanozyme-based electrochemical immunoassay for sensitive detection of human epidermal growth factor receptor 2

The proof-of-concept of sensitive electrochemical immunoassay for the quantitative monitoring of human epidermal growth factor receptor 2 (HER2) is reported. The assay is carried out on iron nitrogen-doped carbon (FeNC) nanozyme-modified screen-printed carbon electrode using chronoamperometry. Introduction of target HER2 can induce the sandwiched immunoreaction between anti-HER2 monoclonal antibody-coated microplate and biotinylated anti-HER2 polyclonal antibody. Thereafter, streptavidin-glucose oxidase (GOx) conjugate is bonded to the detection antibody. Upon addition of glucose, 3,3',5,5'-tetramethylbenzidine (TMB) is oxidized through the produced H2O2 with the assistance of GOx and FeNC nanozyme. The oxidized TMB is determined via chronoamperometry. Experimental results revealed that electrochemical immunosensing system exhibited good amperometric response, and allowed the detection of target HER2 as low as 4.5 pg/mL. High specificity and long-term stability are acquired with FeNC nanozyme-based sensing strategy. Importantly, our system provides a new opportunity for protein diagnostics.

An ultrasensitive label-free fluorescent aptamer sensor based on pH-gated release coumarin for detect HER2

Evaluation of human epidermal growth factor receptor 2 (HER2) molecular markers is a very suitable option for early diagnosis of breast cancer. Metal-organic frameworks (MOFs) have large porosity and surface interactions such as π-π stacking, electrostatics, hydrogen bonding, and coordination. Here, we integrated the HER2 aptamer and fluorescent probe coumarin (COU) with zeolite imidazolic acid framework-8 (ZIF-8) to construct a label-free fluorescent aptamer sensor with pH-gated release of COU. In the presence of the target-HER2, the aptamer adsorbed on the surface of ZIF-8@COU specifically recognizes and falls off the HER2 protein, exposing a portion of the pore size of ZIF-8@COU while reducing the negative charge on the sensor surface, under alkaline hydrolysis conditions, a large number of COU fluorescent molecules can be produced and released in the detection system.The aptamer fluorescence sensor has good detection performance, sensitivity and low background interference, the detection linearity range of HER2 protein is 0.05-10 ng/mL, the detection limit is 0.0005 ng/mL, and it has good recovery rate for the serum detection of clinical breast cancer patients. Therefore, this sensor has high potential in detecting and monitoring HER2 levels for the care and clinical diagnosis of breast cancer patients.

Quantum dot-labeled phage-encoded RBP 55 as a fluorescent nanoprobe for sensitive and specific detection of Salmonella in food matrices

As a commonly pathogenic bacterium, the rapid detection of Salmonella outbreaks and assurance of food safety require a highly efficient detection method. Herein, a novel approach to Salmonella detection using quantum dot-labeled phage-encoded RBP 55 as a fluorescent nanoprobe is reported. RBP 55, a novel phage receptor binding protein (RBP), was identified and characterized from phage STP55. RBP 55 was functionalized onto quantum dots (QDs) to form fluorescent nanoprobes. The assay was based on the combination of immunomagnetic separation and RBP 55-QDs, which formed a sandwich composite structure. The results showed a good linear correlation between the fluorescence values and the concentration of Salmonella (10¹-10⁷ CFU/mL) with a low detection limit of 2 CFU/mL within 2 h. The method was used to successfully detect Salmonella in spiked food samples. This approach can be used for the simultaneous detection of multiple pathogens by labeling different phage-encoded RBPs using polychromatic QDs in the future.

Impact of Nanomedicine in Women's Metastatic Breast Cancer

Metastatic breast cancer is responsible for 90% of mortalities among women suffering from various types of breast cancers. Traditional cancer treatments such as chemotherapy and radiation therapy can cause significant side effects and may not be effective in many cases. However, recent advances in nanomedicine have shown great promise in the treatment of metastatic breast cancer. For example, nanomedicine demonstrated robust capacity in detection of metastatic cancers at early stages (i.e., before the metastatic cells leave the initial tumor site), which gives clinicians a timely option to change their treatment process (for example, instead of endocrine therapy they may use chemotherapy). Here recent advances in nanomedicine technology in the identification and treatment of metastatic breast cancers are reviewed.

A multicolor immunosensor for the visual detection of six sulfonamides based on manganese dioxide nanosheet-mediated etching of gold nanobipyramids

In reality, various sulfonamides (SAs) were alternately used in animal husbandry to avoid generating drug resistance. Thus, it is crucial to develop simple and high-throughput methods for detecting multiple or groups of SAs to realize rapid screening of total SAs residues in foods. We herein developed a sensitive and efficient MnO₂ nanosheets-mediated etching of gold nanobipyramids (AuNBPs), which can generate more vivid color changes, and further fabricated a high-throughput multicolor immunosensor for the visual screening/semi-quantitative detection of 6 different SAs including sulfamethazine (SMZ), sulfamethoxydiazine (SMD), sulfisomidine (SIM), sulfamerazine (SMR), sulfamonomethoxine (SMM) and sulfaquinoxaline (SQ) by using AuNBPs as signal and broad-specificity anti-SAs antibody as a bio-receptor. The immunosensor displays more vivid color changes, and has a lower visual detection limit and excellent specificity. It can be applied to detect as little as 1.0 ng/mL of SMZ, SMD, SMR and 2.0 ng/mL of SIM, SMM, SQ by bare eye observation, and 0.2 ng/mL of above 6 SAs by UV-visible spectrophotometry. The visual detection limit of the immunosensor is much lower than the maximum residue limit of total SAs (100 μg/kg) in edible tissues. The immunosensor was successfully applied to detect SMZ, SMD, SIM, SMR, SMM and SQ in milk with a recovery of 84%-106% and a RSD (n = 5) < 8%. The success of this study provided a promising assay for the on-site rapid screening of SMZ, SMD, SIM, SMR, SMM and SQ in food by bare eye observation. Importantly, the immunosensor may be expended as a general method for the visual screening/semi-quantitative detection of the group of other antibiotics by using the corresponding broad-specificity antibody as a bio-receptor.

Smartphone-Based Photoelectrochemical Immunoassay with Co9S8@ZnIn2S4 for Point-of-Care Diagnosis of Breast Cancer Biomarker

Photoelectrochemical immunoassays incorporating specific antigen-antibody recognition reactions with the photon-electron conversion capabilities of photocatalysts have been developed for biomarker detection, but most involve bulky and expensive equipment and are unsuitable for point-of-care testing. Herein, a portable smartphone-based photoelectrochemical immunoassay was innovatively designed for the on-site detection of breast cancer biomarkers (human epidermal growth factor receptor 2; HER2). The system consists of a split-type immunoassay mode, disposable screen-printed electrode covered with hierarchical Co9S8@ZnIn2S4 heterostructures, an integrated circuit board, and a Bluetooth smartphone equipped with a specially designed app. Using alkaline phosphatase (ALP) catalytic strategy to in situ generate ascorbic acid (AA) for electron-donating toward Co9S8@ZnIn2S4 heterostructures, an immunoreaction was successfully constructed for the HER2 detection in the real sample due to the positive correlation of the photocurrent signal to electron donor concentration. Differential charge density indicates that the formation of Co9S8@ZnIn2S4 heterojunction can facilitate the flow of charges in the interface and enhance the photocurrent of the composite. More importantly, the measured photocurrent signal can be wirelessly transmitted to the software and displayed on the smartphone screen to obtain the corresponding HER2 concentration value. The photocurrent values linearly with the logarithm of HER2 concentrations range spanned from 0.01 ng/mL to 10 ng/mL with a detection limit of 3.5 pg/mL. Impressively, the clinical serum specimen results obtained by the proposed method and the wireless sensing device are in good agreement with the enzyme-linked immunosorbent assay (ELISA).

Paper-based multicolor sensor for on-site quantitative detection of 2,4-dichlorophenoxyacetic acid based on alkaline phosphatase-mediated gold nanobipyramids growth and colorimeter-assisted method for quantifying color

On-site quantitative analysis of pesticides is important for food safety. Colorimetric gold nanobipyramids (AuNBPs) sensors are powerful methods for on-site detection. However, a single quantitative method and the instability of AuNBPs in solution limit the practicability of those sensors. Here, a paper-based multicolor AuNBPs sensor involved a colorimeter-assisted method for quantifying color was developed for quantitative detection of 2,4-dichlorophenoxyacetic acid (2,4-D), a common herbicide. The novelty of this study lies in developing a general paper-based quantitative on-site method (PQOM) for colorimetric AuNBPs sensors. Firstly, a paper-based analytical device (PAD) consisting of a nylon membrane, absorbent cotton layers, and two acrylic plates was fabricated to deposit AuNBPs. We demonstrated the PAD could improve the stability of AuNBPs and the detection sensitivity of AuNBPs sensors. Then, a handheld colorimeter was first used to quantify the color change of AuNBPs on the PAD based on the CIELab color space. Finally, as proof of concept, the PQOM was successfully employed to quantify 2,4-D by combining with an alkaline phosphatase-mediated AuNBPs growth method. In this method, 2,4-D specifically inhibited alkaline phosphatase activity to suppress the generation of l-ascorbic acid, thereby mediating AuNBPs growth. The developed sensor exhibited seven 2,4-D concentration-related colors and detected as low as 50 ng mL-1 2,4-D by naked-eye observation and 18 ng mL-1 2,4-D by a colorimeter. It was applied to detect 2,4-D in the spiked rice and apple samples with good recovery rates (91.8-112.0%) and a relative standard deviation (n = 5) < 5%. The success of this study provides a sensing platform for quantifying 2,4-D on site.

A high-resolution colorimetric immunoassay for tyramine detection based on enzyme-enabled growth of gold nanostar coupled with smartphone readout

In this work, a specific monoclonal antibody against tyramine was produced based on a new hapten design. Then, we developed a high-resolution multicolor colorimetric immunoassay for tyramine based on this antibody by integrating enzyme-induced multicolor generation with smartphone-assistant signal readout. The multicolor generation is due to the shift of the local surface plasmon resonance band of gold nanostructure controlled by alkaline phosphatase-induced the growth of gold nanostars. Quantitative detection of tyramine was achieved via analyzing the red/blue channel values of assay solution's image taken by a smartphone with the support of a color recognizer application. The limit of detection of this immunoassay for tyramine detection in beef, pork and yoghurt was 19.7 mg/kg or L. The average recoveries were between 83 % and 103 %., and the results were validated by high performance liquid chromatography to be reliable. Overall, this developed immunoassay provides a promising platform for on-site detection of tyramine.

Digital image colorimetry in combination with chemometrics for the detection of carbaryl based on the peroxidase-like activity of nanoporphyrins and the etching process of gold nanoparticles

Carbaryl is a typical carbamate pesticide that plays an essential role in agricultural production, but its residues cause serious harm to the environment and human health. Here, we developed a polychromatic colorimetric sensor based on ZnTPyP-DTAB peroxidase activity and gold nano-bipyramids (Au NBPs) etching to detect carbaryl. ZnTPyP-DTAB catalyzes the decomposition of H₂O₂ to hydroxyl radicals, and Au NBPs are etched. The coordination of zinc and nitrogen in nanometer porphyrins was affected by the steric effects of carbaryl, which resulted in decreased activity of ZnTPyP-DTAB peroxidase. The detection limit of carbaryl was 0.26 mg/kg. The recoveries of carbaryl in reaal sample ranged from 91 % to 107% (RSD ≤ 0.7%). The sensor platform displayed a series of high-resolution multicolor variations of rainbow colors within the above concentration range. The rich color variation facilitates the acquisition of digital images. RGB value transformation combined with partial least squares regression model can accurately and quantitatively detect carbaryl in vegetables, fruits and Chinese medicinal materials.

Preparation of bimetal–polydopamine organic frameworks with core–shell structure and their application in HER2 detection

Human epidermal growth factor receptor 2 (HER2) is one of the specific markers of breast cancer, which is of great significance to the early diagnosis and prognosis of breast cancer.

An NADH-selective and sensitive fluorescence probe to evaluate living cell hypoxic stress

Cellular disease and senescence are often accompanied by an imbalance in the local oxygen supply. Under hypoxia, mitochondrial NADH and FADH₂ cannot be oxidized by the mitochondrial electron transport chain, which leads to the accumulation of reducing equivalents and subsequent reduction stress. Detecting changes in intracellular NADH levels is expected to allow an assessment of stress. We synthesized a red fluorescent probe, DPMQL1, with high selectivity and sensitivity for detecting NADH in living cells. The probe DPMQL1 has strong anti-interference abilities toward various potential biological interferences, such as metal ions, anions, redox species, and other biomolecules. In addition, its detection limit can reach the nanomolar level, meaning it can display small changes in NADH levels in living cells, so as to realize the evaluation of cell-based hypoxic stress.

Three-dimensional porous calcium alginate fluorescence bead-based immunoassay for highly sensitive early diagnosis of breast cancer

A sensitive biosensor capable of detecting trace concentrations of several cancer biomarkers in clinical samples is critical for early detection of cancer because different cancer biomarkers may be expressed at different stages of cancer. Previous multiplex studies using microarrays or color-coded beads had limited multiplex detection in a single well, and difficulty in optimizing and unifying the incubation parameters for all tests made in different wells had posed challenges to small sample size and lengthened assay time. Herein, we proposed a novel approach to achieve multiplex analysis on a single three-dimensional porous calcium alginate bead. Because of the high surface area to volume ratio of the calcium alginate immuno-bead, the sensitivity and linear dynamic range of the as-proposed multiplex analysis method are significantly improved. Based on the direct sandwich immunoassay principle, dual-capturing antibodies were encapsulated into a single 3D porous calcium alginate bead as a proof-of-concept for multiplexity detection of serum-HER2 and serum-CA125 breast cancer biomarkers. High sensitivity was attained, with LODs of 0.004 ng mL^-1 for serum HER2, and 0.005 U mL^-1 for serum CA125, both of which are below the clinical cutoff values, enabling for early breast cancer diagnosis. Stability tests revealed that the 3D immuno-beads were stable at 4 °C and room temperature (25 °C) for at least 14 days. Most importantly, the results obtained using the developed system were in good agreement with those obtained using standard methods while analyzing real clinical samples. In addition, the analysis required only approximately 30 min, which was much less time than typical ELISA techniques. When endogenous interferences were introduced, no cross-reactivity was observed. We anticipate this approach to be potentially used in the multiplex assays and biosensors.

Integrating multiple hybridization chain reactions on gold nanoparticle and alkaline phosphatase-mediated in situ growth of gold nanobipyramids: An ultrasensitive and high color resolution colorimetric method to detect the mecA gene of Staphylococcus aureus

Colorimetry has been considered as a potential instrument-free platform for point-of-care genomic detection. However, it is limited by the poor sensitivity and low color resolution. Herein, we report a high-resolution colorimetric biosensor based on multiple hybridization chain reactions (HCRs) on gold nanoparticle (AuNP) and alkaline phosphatase (ALP)-mediated in situ growth of gold nanobipyramids (AuNBPs) for ultrasensitive detection of the Staphylococcus aureus (S. aureus) mecA gene. In our design, target DNA is hybridized with capture hairpin DNA on magnetic beads and then amplified by multiple HCRs on AuNP. Since biotin-labeled hairpin-structured nucleic acids are utilized to conduct HCRs, together with the large specific surface area of AuNP, the biotin- and streptavidin- based reaction results in a large amount of ALP on AuNP. With the aid of NADPH, ALP-mediated in situ growth of AuNBPs is observed, and a series of rainbow-like colors are associated with different target DNA concentrations. Through the multiple-amplification strategy produced by AuNP, HCRs, and enzymatic reactions, the target DNA as low as 2.71 pM can be detected with high specificity. Moreover, this method has been successfully applied to detect the mecA gene extracted from S. aureus. Therefore, the proposed method holds great potential in clinical diagnosis.

Fluorescent enzyme-linked immunosorbent assay based on alkaline phosphatase-responsive coordination polymer composite

The fabrication of alkaline phosphatase (ALP)-responsive coordination polymer (CP) composite is demonstrated for establishing a fluorescent immunoassay. The CP composite (ThT@GMP/Eu) was synthesized by encapsulating thioflavin T (ThT) into the CP host that was composed of europium ion (Eu³⁺) and guanine monophosphate (GMP). The ThT@GMP/Eu composite shows a strong fluorescence in aqueous solution due to the confinement effect of GMP/Eu CPs, which restricts the conformational rotation of ThT. However, upon the addition of ALP, the structure of GMP/Eu CPs was disrupted to release ThT into solution. This results in the quenching of the fluorescence of ThT@GMP/Eu. The fluorescence of ThT@GMP/Eu has a linear response that covers 0.8 to 120 mU/mL ALP with a detection limit of 0.26 mU/mL and exhibits excellent specificity towards ALP against other enzymes. On this basis, inspired by the wide application of ALP as an enzyme label in enzyme-linked immunosorbent assay (ELISA), an ALP-based fluorescent immunoassay was further developed for the detection of mouse immunoglobulin G (mIgG). The developed immunoassay displays a linear fluorescent response towards mIgG from 0.8 to 100 ng/mL, and the detection limit is 0.16 ng/mL. The fluorescent immunoassay was successfully applied to the determination of mIgG in serum samples. Schematic of the responsivity of ThT@GMP/Eu to ALP that hydrolyzes GMP to release ThT, which leads to fluorescent quenching, and its application in the construction of a fluorescent immunoassay for mIgG determination.

Multifunctional nanoparticles as optical biosensing probe for breast cancer detection: A review

Optical biosensors show attractive performance in medical sensing in the event of using different nanoparticles in their design. Owing to their unique optical characteristics and biological compatibility, gold nanoparticles (GNPs), silver nanoparticles (AgNPs), bimetallic nanoparticles and magnetic nanoparticles have been broadly implemented in making sensing tools. The functionalization of these nanoparticles with different components provides an excellent opportunity to assemble selective and sensitive sensing materials to detect various biological molecules related to breast cancer. This review summarizes the recent application of optical biosensing devices based on nanomaterials and discusses their pros and cons to improve breast cancer detection in real samples. In particular, the main constituent elements of these optical biosensors including recognition and transducer elements, types of applied nanostructures, analytical sensing procedures, sensor detection ranges and limit of detection (LOD), are expressed in detail.

New application of a traditional method: colorimetric sensor array for reducing sugars based on the in-situ formation of core-shell gold nanorod-coated silver nanoparticles by the traditional Tollens reaction

An effective and robust colorimetric sensor array for simultaneous detection and discrimination of five reducing sugars (i.e., glyceraldehyde (Gly), fructose (Fru), glucose (Glu), maltose (Mal), and ribose (Rib)) has been proposed. In the sensor array, two negatively charged polydielectrics (sodium polystyrenesulfonate (NaPSS) and sodium polymethacrylate (NaPMAA)), which served as the sensing elements, were individually absorbed on the surface of the cetyltrimethylammonium bromide (CTAB)-coated gold nanorods (AuNR) with positive charges through electrostatic action, forming the designed sensor units (NaPSS-AuNR and NaPMAA-AuNR). In the presence of Tollens reagent (Ag(NH₃)₂OH), Ag⁺ was absorbed on the surface of negatively charged NaPSS-AuNR and NaPMAA-AuNRs. When confronted with differential reducing sugars, different reducing sugars exhibited differential levels of deoxidizing abilities toward Ag⁺, thus Ag⁺ was reduced to diverse amounts of silver nanoparticles (AgNPs) in situ to form core-shell AuNR@AgNP by the traditional Tollens reaction method, leading to distinct colorimetric response patterns (value of A_S/A_L (the ratio of absorbance at 360 nm to that at 760 nm in Ag⁺-NaPMAA-AuNR, and the ratio of absorbance at 360 nm to that at 740 nm in Ag⁺-NaPSS-AuNR)). These response patterns are characteristic for each reducing sugar, and can be quantitatively distinguished by linear discriminant analysis (LDA) at concentrations as low as 10 nM with relative standard deviation (RSD) of 4.11% (n = 3). The practicability of this sensor array has been validated by recognition of reducing sugars in serum and urine samples. A colorimetric sensor array for reducing sugar discrimination based on the reduction of Ag⁺ and in situ formation of AuNR@AgNP.

Dual-Modal Immunosensor with Functionalized Gold Nanoparticles for Ultrasensitive Detection of Chloroacetamide Herbicides

Convenient and ultrasensitive detection of pesticides is demanded for healthcare and environmental monitoring, which can be realized with a dual-modal strategy. In this paper, based on a biotin-labeled IgG-modified gold nanoparticle (AuNP@IgG-bio) probe, a dual-modal immunosensor was proposed for detecting chloroacetamide herbicides. This platform is relied on the dephosphorylation of ascorbic acid 2-phosphate (AA2P) by alkaline phosphatase (ALP). In addition to this process, ascorbic acid (AA)-triggered deposition of silver on gold nanostars (AuNSs) and the fluorogenic reaction of dehydrogenated AA and o-phenylenediamine (OPD) occur sequentially. Thus, the dual readout of the color change of red-green-blue (RGB) and fluorescence generation in situ induced by crystal growth can be used. The limits of detection (LODs) were as low as 1.20 ng/mL of acetochlor (ATC), 0.89 ng/mL of metolachlor, 1.22 ng/mL of propisochlor, and 0.99 ng/mL of their mixture by a smartphone and 0.44 ng/mL of ATC, 1.59 ng/mL of metolachlor, 2.80 ng/mL of propisochlor, and 0.72 ng/mL of their mixture by a spectrofluorometer. The recoveries from corn were 91.4-105.1% of the colorimetric mode and 92.4-106.2% of the fluorescent mode. Due to its simple observation mode and good performance, this dual-modal immunosensor possesses considerable application prospects.

Multicolor visual screening of total dithiocarbamate pesticides in foods based on sulfydryl-mediated growth of gold nanobipyramids

Dithiocarbamates (DTCs) pesticides were extensively used as fungicides in a variety of crops during their growth, storage and shipment. The DTCs residue in foods will seriously harm human health. In this study, a novel multicolor colorimetric sensor was developed for visual screening of total DTCs (total of ziram, thiram and zineb) based on sulfhydryl-mediated growth of gold nanobipyramids (AuNBPs). We demonstrated that DTCs can absorb on AuNBPs seed's surface via the formation of Au-S bonds and thus impede the 8-hydroxyquinoline (8-HQ)-promoted AuNBPs growth, which generates DTCs concentration-corresponding color changes. The developed sensor has vivid color changes, short analysis time, higher sensitivity and excellent specificity. It can be used to detect as low as 50 nM of total DTCs by bare eye observation and 17-18 nM of total DTCs by UV-visible spectrometry. By using the multicolor sensor, we have successfully screened total DTCs in apple and black tea by bare eye observation, and detected total DTCs in apple and black tea by UV-visible spectrometry with a recovery of 90%-104% and a relative standard deviation (RSD, n = 5) < 5%. The results obtained with our method consisted well with those obtained with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), verifying that our method had good accuracy and reliability. Especially, the visual detection limit of our method is much lower than the maximum residue limit of total DTCs in vegetable and fruits. All above features make our sensor a promising method for rapid on-site screening of total DTCs in vegetable and fruits by only bare eye observation.

Multifunctional Gold Nanoparticles: A Novel Nanomaterial for Various Medical Applications and Biological Activities

Nanotechnology has become a trending area in science and has made great advances with the development of functional, engineered nanoparticles. Various metal nanoparticles have been widely exploited for a wide range of medical applications. Among them, gold nanoparticles (AuNPs) are widely reported to guide an impressive resurgence and are highly remarkable. AuNPs, with their multiple, unique functional properties, and easy of synthesis, have attracted extensive attention. Their intrinsic features (optics, electronics, and physicochemical characteristics) can be altered by changing the characterization of the nanoparticles, such as shape, size and aspect ratio. They can be applied to a wide range of medical applications, including drug and gene delivery, photothermal therapy (PTT), photodynamic therapy (PDT) and radiation therapy (RT), diagnosis, X-ray imaging, computed tomography (CT) and other biological activities. However, to the best of our knowledge, there is no comprehensive review that summarized the applications of AuNPs in the medical field. Therefore, in this article we systematically review the methods of synthesis, the modification and characterization techniques of AuNPs, medical applications, and some biological activities of AuNPs, to provide a reference for future studies.