A novel SERS sensor for the ultrasensitive detection of kanamycin based on a Zn-doped carbon quantum dot catalytic switch controlled by nucleic acid aptamer and size-controlled gold nanorods

Chemiluminescence detection of kanamycin by DNA aptamer regulating peroxidase-like activity of Co3O4 nanoparticles

Kanamycin (KAN) is widely used as a growth hormone analog and an antibacterial agent. However, abuse of this substance has resulted in the accumulation of excessive residue levels in foods of animal origin, which presents a significant risk to human health. A chemiluminescent aptasensor was constructed for the rapid quantitative detection of KAN by combining the properties of Co3O4 nanoparticles (Co3O4 NPs) nanozyme activity and DNA aptamer with high specificity. The DNA aptamer/Co3O4 NPs nanozyme regulated the chemiluminescence signal by exploiting the chemiluminescent properties of luminol oxidation by H2O2. Specific binding of KAN to the aptamer led to the formation of a steric hindrance block in the solution, which inhibited the activity of nanozyme and reduced signal intensity. The degree of signal reduction is related to the concentration of KAN. Under optimal conditions, there was good linearity between KAN concentration and chemiluminescence signal intensity in the range of 0.5-8.0 μΜ, with a detection limit of 0.26 μΜ. The detection system performed well in the presence of competing antibiotics and was virtually unaffected. The method was also suitable for the detection of KAN in milk samples with sample recoveries of 97.8%-99.1%. The chemiluminescence sensor has the advantages of low cost, specificity, and sensitivity, and does not require an external light source or modification of the nucleic acid aptamer which makes it a promising candidate for applications in the field of food detection.

Metal-doped carbon dots for biomedical applications: From design to implementation

Carbon dots (CDs), as a new kind of fluorescent nanomaterials, show great potential for application in several fields due to their unique nano-size effect, easy surface functionalization, controllable photoluminescence, and excellent biocompatibility. Conventional preparation methods for CDs typically involve top-down and bottom-up approaches. Doping is a major step forward in CDs design methodology. Chemical doping includes both non-metal and metal doping, in which non-metal doping is an effective strategy for modulating the fluorescence properties of CDs and improving photocatalytic performance in several areas. In recent years, Metal-doped CDs have aroused the interest of academics as a promising nano-doping technique. This approach has led to improvements in the physicochemical and optical properties of CDs by altering their electron density distribution and bandgap capacity. Additionally, the issues of metal toxicity and utilization have been addressed to a large extent. In this review, we categorize metals into two major groups: transition group metals and rare-earth group metals, and an overview of recent advances in biomedical applications of these two categories, respectively. Meanwhile, the prospects and the challenges of metal-doped CDs for biomedical applications are reviewed and concluded. The aim of this paper is to break through the existing deficiencies of metal-doped CDs and fully exploit their potential. I believe that this review will broaden the insight into the synthesis and biomedical applications of metal-doped CDs.

SERS detection of apramycin and kanamycin through sliver nanoparticles modified with β-cyclodextrin and α-iron oxide

Using sliver nanoparticles modified with β-cyclodextrin and α-iron oxide (β-CD/α-Fe2O3@AgNPs) as surface-enhanced Raman spectroscopy (SERS) substrate, two sensitive methods for detecting apramycin and kanamycin were established. The synthesized β-CD/α-Fe2O3@AgNPs were characterized through ultraviolet visible (UV-vis) spectroscopy, transmission electron microscope (TEM), X-ray diffraction (XRD) and thermogravimetric analyses (TGA). The interactions of the two drugs and substrate were researched by UV-vis absorption and fourier transform infrared (FT-IR). The linear relationship between apramycin/kanamycin and SERS intensity was observed. The limits of detection (LODs) (S/N = 3) were 3.42 and 0.31 nmol/L. The two SERS methods were effectively applied to detect apramycin and kanamycin in beef samples and commercial injection. The recoveries were 96.84 - 102.20% with relative standard deviations (RSD) of 0.6---4.0% for apramycin and 95.67 - 103.18% with RSD of 1.4 - 2.5% for kanamycin, respectively.

Design of competition nanoreactor with shell-isolated colloidal plasmonic nanomaterials for quantitative sensor platform

Shell-isolated colloid plasmonic nanomaterials-based nanoreactor is a well-established platform widely applied in catalyst or Surface Enhanced Raman Scattering (SERS) sensors. The potentials versatility of nanoreactor platform is mainly implemented by the well-defined and tailorable structure of colloid plasmonic nanomaterials. Currently, a competitive conjugative-mediated nanoreactor is introduced to determine glucose with SERS. Glucose-conjugating nanoreactor, as convertors of the sensors, are constructed by coordinated deposition colloidal gold nanoparticles with sodium nitroprusside framework (Au@SNF) and covalently bonded 4-mercaptopyridine (4-Mpy) with self-assembly strategy. The nanoreactor contained the signal-amplifier Au@SNF NPs, conjugative-mediated signal receiver 4-Mpy, and signal internal standard molecular CN^-. In addition to well-defined morphology and functionality, conjugative-mediated and internal standards method are also employed to benefit the nanoreactor. The two-parameter strategy significantly improves the signal indication and correction. Using this proposed platform, the competitive-mediated nanoreactor provides a quantitative SERS detection of glucose, and extends the applicability of SERS in more complicated and reproducibility analysis. Meanwhile, the nanoreactor based sensors also exhibited better properties to detect glucose in various food samples and bio-samples which provided strongly appliance for glucose sensors.

A surface-enhanced Raman scattering sensor for the detection of benzo[a]pyrene in foods based on a gold nanostars@reduced graphene oxide substrate

In this study, a simple and sensitive surface-enhanced Raman scattering (SERS) sensor based on gold nanostars@reduced graphene oxide (AuNS@rGO) was successfully developed for the detection of benzo[a]pyrene in foods. The detection strategy involved benzo[a]pyrene adsorption on reduced graphene oxide, followed SERS detection of adsorbed molecules. Owing to the large electric fields generated by the gold nanostars under laser irradiation, which greatly amplified the Raman signals of benzo[a]pyrene, very high sensitivity for the target analyte was achieved. Under optimized conditions, the SERS sensor exhibited a wide linear detection range for benzo[a]pyrene (from 0.1 μg L^-1 to 10000 μg L^-1), with a low limit of detection of 0.0028 μg L^-1. Chicken samples spiked with benzo[a]pyrene were assayed using the sensor, with recoveries ranging from 89.20% to 100.80%. The benzo[a]pyrene content in roasted mutton sample was quantified using the SERS sensor and a reversed-phase high-performance liquid chromatography method, with similar results being obtained.

A fluorescent assay for sensitive detection of kanamycin by split aptamers and DNA-based copper/silver nanoclusters

Kanamycin was a group of essential antibiotics generally served in treating infections of animals which leached into the environment residual in food, causing health concerns. Thus, selective and sensitive monitoring of kanamycin was significant for food safety. In this work, split aptamers were used as templates to prepare fluorescent Cu/Ag NCs for detection of kanamycin. According to the impressive affinity of the aptamer to kanamycin, two different detection modes were designed using kanamycin aptamer as a recognition molecule, in which one was to combine split aptamer Apt-1 with Apt-2 to form an entangled DNA as a Cu/Ag NCs template, the other was to associate the normal aptamer after encirclement to form Cu/Ag NCs templates. After the addition of kanamycin, the fluorescence signals of the Cu/Ag NCs synthesized in the two modes were both enhanced, but the approach with split aptamer exhibited a superior observable sensitivity than that of the normal type. The detection range showed a well linear relationship between 80 nM and 10 μM when the emission wavelength was 560 nm, and the detection limit was 13.3 nM. In addition, when streptomycin, oxytetracycline, chloramphenicol and chlortetracycline were involved in the selective interference experiment under the same conditions, the fluorescence intensity of the system performed no significant changes. The results demonstrated that this method possessed favorable specificity and selectivity for the assay of kanamycin, proficiently achieving efficient, rapid and sensitive evaluation of kanamycin in the milk samples.

SERS- and absorbance-based catalytic assay for determination of isocarbophos using aptamer-modified FeMOF nanozyme and in situ generated silver nanoparticles

A new Fe metal-organic framework-loaded liquid crystal 4-octoxybenzoic acid (FeMOF@OCTB) nanosol was synthesized using 1,3,5-phthalic acid, ferrous sulfate, and OCTB as precursors. The FeMOF@OCTB exhibits good stability and strong catalytic effect for the polyethylene glycol 400-Ag (I) indicator reaction, which was evaluated rapidly by the slope procedure. The generated silver nanoparticles have a strong surface-enhanced Raman scattering (SERS) effect and a surface plasmon resonance absorption (Abs) peak at 420 nm. This new bimodal nanosilver indicator reaction was coupled with the isocarbophos (IPS)-aptamer (Apt) reaction. A FeMOF@OCTB nanocatalytic amplified-SERS/Abs bimodal Apt assay for IPS was established. The SERS assay can detect IPS in the concentration range 0.02-1.2 nM, with a detection limit of 0.010 nM. It has been applied to the determination of IPS in rice samples. The relative standard deviation was 4.4-5.8%, and the recovery was 97.7-104%. An Ag nanosol plasmon SERS/Abs dimode aptamer assay was fabricated for trace isocarbophos, based on highly catalysis MOF@OCTB nanoenzyme.

[Surface-enhanced Raman detection of deoxynivalenol allenol in agricultural products]

Fungal toxins are secondary metabolites of fungi. Food is highly susceptible to contamination by various fungal species that produce fungal toxins during production and storage. Fungal toxins can cause either acute or chronic poisoning from long-term, low-dose ingestion. Therefore, fungal toxins have become a topic of international interest as a food safety issue. Deoxynivalenol (DON) is a single-terminal sporam toxin produced predominantly by Fusarium graminae and Fusarium pinkosa. DON is globally one of the most common fungal toxins contaminating grain, food, and feed. Various methods have been applied for screening and detecting DON; however, these methods utilize expensive instruments and entail complex operations, poor repeatability, and low sensitivity. Therefore, the development of a simpler, more rapid, and sensitive sensing technology for DON detection is important for applications within the agriculture and food industry. Recently, surface-enhanced Raman scattering (SERS) has become a rapidly developing spectral analysis technology with unique advantages, including high sensitivity, high throughput, and rapid response rates. Therefore, attempts have been made to apply the SERS technique to detecting DON. However, due to the limitations concerning SERS substrates, the currently established SERS method exhibits serious problems, including low sensitivity and weak anti-interference ability, and cannot meet the requirements of sample detection. Recently, our group has prepared aggregated silver nanoparticles (a-AgNPs/CDs) with high SERS activity by using single-layer carbon-based dots (CDs) as a capping agent. Moreover, the obtained materials (a-AgNPs/CDs) were combined with hydrogel technology to prepare novel hydrogel SERS chips. The obtained SERS chips exhibited several advantages over traditional SERS substrates, such as high sensitivity, long-term stability, improved uniformity, and strong anti-interference capabilities. Herein, a novel SERS method for rapid screening and detection of DON in grains was established using a portable Raman spectrometer based on the developed hydrogel SERS chips. The main experimental conditions were optimized before the SERS detection of DON; this included the optimization of the hydrogel SERS chip soaking temperature and time in the DON solution. It was found that the optimal soaking temperature and time were 40 ℃ and 5 min, respectively. Under the optimal SERS detection conditions, the linear response range of DON was 1-10000 μg/kg (correlation coefficient (R2)=0.9967), and the limit of detection (LOD) was 0.14 μg/kg. Due to the unique pore size structure of the hydrogel, common sugar, protein, oil, pigment, and other interfering substances in the sample matrix were blocked outside the hydrogel. Therefore, only simple extraction was required while detecting complex samples. This method was applied to detecting DON in wheat flour, yielding recoveries of 97.3%-103% with relative standard deviations of 4.2%-5.0%. The established SERS method for DON detection exhibits a broader response range, high sensitivity, good repeatability, rapid response, simple operation, and strong anti-interference capability. This shows that the laboratory-constructed hydrogel SERS chip has excellent potential for rapid screening and detection of biotoxins in food.

Dual-mode photoelectrochemical/electrochemical sensor based on Z-scheme AgBr/AgI-Ag-CNTs and aptamer structure switch for the determination of kanamycin

A "signal-on" dual-mode aptasensor based on photoelectrochemical (PEC) and electrochemical (EC) signals was established for kanamycin (Kana) assay by using a novel Z-scheme AgBr/AgI-Ag-CNTs composite as sensing platform, an aptamer structure switch, and K₃[Fe(CN)₆] as photoelectron acceptor and electrochemical signal indicator. The aptamer structure switch was designed to obtain a "signal-off" state, which included an extended Kana aptamer (APT), one immobilized probe (P1), and one blocking probe (P2) covalently linked with graphdiyne oxide (GDYO) nanosheets. P1, P2, and aptamer formed the double helix structure, which resulted in the inhibited photocurrent intensity because of the weak conductivity of double helix layer and serious electrostatic repulsion of GDYO towards K₃[Fe(CN)₆]. In the presence of Kana, APT specifically bound to the target and dissociated from P1 and P2, and thus, a "signal-on" state was initiated by releasing P2-GDYO from the platform. Based on the sensing platform and the aptamer structure switch, the dual-mode aptasensor realized the linear determination ranges of 1.0 pM-2.0 μM with a detection limit (LOD) of 0.4 pM (for PEC method) and 10 pM-5.0 μM with a LOD of 5 pM (for EC method). The aptasensor displayed good application potential for Kana test in real samples.

Progress on aptamer-based SERS sensors for food safety and quality assessment: methodology, current applications and future trends

It is well known that food safety has aroused extensive attentions from governments to researchers and to food industries. As a versatile technology based on molecular interactions, aptamer sensors which could specifically identify a wide range of food contaminants have been extensively studied in recent years. Surface-enhanced Raman spectroscopy integrated aptamer combines the advantages of both technologies, not only in the ability to specifically identify a wide range of food contaminants, but also in the ultra-high sensitivity, simplicity, portable and speed. To provide beneficial insights into the evaluation techniques in the field of food safety, we offer a comprehensive review on the design strategies for aptamer-SERS sensors in different scenarios, including non-nucleic acid amplification methods ("on/off" mode, sandwich mode, competition model and catalytic model) and nucleic acid amplification methods (hybridization chain reaction, rolling circle amplification, catalytic hairpin assembly). Meanwhile, a special attention is paid to the application of aptamer-SERS sensors in biological (foodborne pathogenic, bacteria and mycotoxins) and chemical contamination (drug residues, metal ions, and food additives) of food matrix. Finally, the challenges and prospects of developing reliable aptamer-SERS sensors for food safety were discussed, which are expected to offer a strong guidance for further development and extended applications.

Flexible surface-enhanced Raman scatting substrates: recent advances in their principles, design strategies, diversified material selections and applications

Surface-enhanced Raman scattering (SERS) is widely used as a powerful analytical technology in cutting-edge areas such as food safety, biology, chemistry, and medical diagnosis, providing ultra-fast, ultra-sensitive, nondestructive characterization and achieving ultra-high detection sensitivity even down to the single-molecule level. Development of Raman spectroscopy is strongly dependent on high-performance SERS substrates, which have long evolved from the early days of rough metal electrodes to periodic nanopatterned arrays building on solid supporting substrates. For rigid SERS substrates, however, their applications are restricted by sophisticated pretreatments for detecting solid samples with non-planar surfaces. It is therefore essential to reassert the principles in constructing flexible SERS substrates. Herein, we comprehensively review the state-of-the-art in understanding, preparing and using flexible SERS. The basic mechanisms behind the flexible SERS are briefly outlined, typical design strategies are highlighted and diversified selection of materials in preparing flexible SERS substrates are reviewed. Then the recent achievements of various interdisciplinary applications based on flexible SERS substrates are summarized. Finally, the challenges and perspectives for future evolution of flexible SERS and their applications are demonstrated. We propose new research directions focused on stimulating the real potential of SERS as an advanced analytical technique for commercialization.

A New Dual-peak Fluorescent Probe for Water Content Detection Made From Taxus

In this paper, the leaves of Taxus were used as the sole carbon source, and two kinds of carbon dots blue and red, with different properties, were synthesized by the hydrothermal method under different conditions. The red carbon dots were quenched in the water, and the blue carbon dots had stable fluorescence properties in water environment. The bimodal fluorescence probe formed by mixing could accurately and stably measure the water content in ethanol, which was in the range of 82.5%-100%, is highly correlated with the fluorescence intensity ratio (I₄₈₁/I₆₇₈) of mixed carbon dots under 390 nm excitation light, with R² = 0.995 and the detection limit as low as 0.31%. The experimental materials are environmentally friendly, low in cost, and simple to operate, as well as the water content measured by proportional fluorescence has high accuracy, which provides a new method for measuring moisture in ethanol.

Novel Dual-Signal Electrochemiluminescence Aptasensor Involving the Resonance Energy Transform System for Kanamycin Detection

Based on luminol-capped Pt-tipped Au bimetallic nanorods (NRs) (L-Au-Pt NRs) as the anode emitter and SnS₂ quantum dots (QDs) hybrid Eu metal organic frameworks (MOFs) (SnS₂ QDs@Eu MOFs) as the cathode emitter, a dual-signal electrochemiluminescence (ECL) platform was designed for the ultrasensitive and highly selective detection of kanamycin (KAN). Using a dual-signal output mode, the ratiometric ECL aptasensor largely eliminates false-positives or false-negatives by self-calibration in the KAN assay process. To stimulate the resonance energy transform (RET) system, the KAN aptamer and complementary DNA are introduced for conjugation between the donor and acceptor. With the specific recognition of target KAN by its aptamer, L-Au-Pt NRs-apt partially peels off from the electrode surface. Eventually, the RET system is removed, leading to an increasing cathode signal and a decreasing anode signal. In view of this phenomenon, the ratiometric aptasensor can quantify KAN from 1 pM to 10 nM with a low detection limit of 0.32 pM. This dual-signal ECL aptasensor exhibits great practical potential in environmental monitoring and food safety.