Engineered "hot" core-shell nanostructures for patterned detection of chloramphenicol

Electrochemical/fluorescent dual-mode aptasensor based on 3D porous AuNPs/MXene for detection of ultra-trace mercury (Hg2+)

In this work, the dual-mode aptasensor based on 3D porous AuNPs/MXene using "turn-on" electrochemical method and "turn-off" fluorescent strategy was fabricated. Here, 2D MXene was processed into 3D porous MXene by sacrificial polymethylmethacrylate (PMMA) spherical template. And the meteor hammer-like AuNPs which had good electrochemical properties and quenching effect on fluorescence was synthesized by single electrodeposition. Dual-signal labeled Nile Blue (NB) was in situ grafted to the Hg2+ aptamer ends of 3D porous AuNPs/MXene/GCE, and an efficient and sensitive signal interface was constructed to realize the sensitive detection of Hg2+. 3D porous AuNPs/MXene had the advantages of large specific surface area, excellent electron transmission performance and signal amplification. The experimental results indicated that this sensor exhibited high sensitivity to Hg2+ in both electrochemical and fluorescent sensing, with detection limits of 2.69 fM and 1.60 fM, respectively. Further, the dual-mode aptasensor can ensure the detection accuracy and target quantization. The dual-mode aptasensor has been successfully applied to the ultra-trace detection of Hg2+ in actual water samples, which shows the potential of aptamer sensor in detecting heavy metal ions in environmental monitoring.

Ultrasensitive detection strategy for CAP by molecularity imprinted SERS sensor based on multiple synergistic enhancement of SiO2@AuAg with MOFs@Au signal carrier

Chloramphenicol (CAP) residue in food can cause great harm to human health, it is important to develop a rapid and sensitive method to detect CAP. Here, molecularly imprinted polymer (MIP) was combined with metal-organic frameworks@Au (MOFs@Au) collaborative construction surface-enhanced Raman spectroscopy (SERS) based aptasensor for CAP ultrasensitive detection. MOFs@Au first carried the Raman signal molecule toluidine blue (TB) and aptamer to form MOFs@Au@TB@Apt. In addition, rMIP (CAP was removed) was dropped onto the uniform three-dimensional (3D) SERS substrate SiO2@AuAg to form SiO2@AuAg@rMIP. In the presence of target CAP, it could be specifically captured with rMIP by covalent interaction and was recognised by the aptamer. During this time, SiO2@AuAg@rMIP@CAP could selectively connect MOFs@Au@TB@Apt to realise synergistic enhance the Raman signal. Based on this principle, the proposed SERS aptasensor exhibits excellent sensitivity with a detection limit of 7.59×10-13 M for CAP, providing a new strategy for trace detection in food.

On-site detection of chloramphenicol in fish using SERS-based magnetic aptasensor coupled with a handheld Raman spectrometer

In recent years, the rapid detection of chloramphenicol (CAP) has become a market demand due to its high toxicity. In this study, for the first time, a portable surface-enhanced Raman scattering (SERS) aptasensor for the rapid and on-site detection of chloramphenicol (CAP) residues in fish was developed. Fe3O4@Au nanoflowers combined with sulfhydryl (SH)-CAP aptamer complementary DNA acted as capture probes. SH-CAP aptamer modified Au@Ag nanoparticles (Au@Ag NPs) embedded with 4-mercaptobenzoic acid (4-MBA) were served as reporter probes. The strongest Raman intensity was produced due to the coupling of Fe3O4@Au nanoflowers (Fe3O4@Au NFs) and Au@Ag NPs. For CAP detection, a wide linear range from 0.001 to 1000 μg/L, with an R2 of 0.9805, was obtained. The limit of detection was determined to be 0.87 ng/L. The SERS aptasensor showed excellent performance for analytical applications for real fish samples. Compared with the conventional HPLC method, the developed SERS aptasensor coupled with a handheld Raman spectrometer had flexible application and avoided the limitations of complex operating conditions. It should be a promising portable analytical tool for analysis of drug residues in the field.

Preparation of in-situ nitrogen-doped lignin-based porous carbon and its efficient adsorption of chloramphenicol in water

Porous carbon is an excellent absorbent for pollutants in water. Here, we report a breakthrough in performance of porous carbon based on lignin prepared using sodium lignosulfonate (SLS), potassium carbonate and melamine as precursor, activator and nitrogen source, respectively. A series of characterization tests confirmed that in-situ nitrogen doping greatly enhanced porous structure, resulting in a specific surface area of 2567.9 m² g^-1 and total pore volume of 1.499 cm³ g^-1, which is nearly twice that of non-nitrogen-doped porous carbon. Moreover, adsorption experiments revealed that at 303 K, the saturated adsorption capacity of chloramphenicol was as high as 713.7 mg g^-1, corresponding to an improvement of 33.7%. Further, the prepared porous carbon exhibited a strong anti-interference against metal ions and humic acid. The adsorption process was confirmed to be an endothermic reaction dominated by physical adsorption, indicating that an increase in temperature is conducive to adsorption. The results of this study show that nitrogen-doped lignin-based porous carbon prepared by in-situ doping is a promising material to significantly alleviate water pollution owing to its low cost, excellent pore structure and good adsorption properties.

Microbial Acoustical Analyzer for Antibiotic Indication

In this study, a compact acoustic analyzer for express analysis of antibiotics based on a piezoelectric resonator with a lateral electric field and combined with a computer was developed. The possibility of determining chloramphenicol in aqueous solutions in the concentration range of 0.5-15 μg/mL was shown. Bacterial cells that are sensitive to this antibiotic were used as a sensory element. The change in the electrical impedance modulus of the resonator upon addition of the antibiotic to the cell suspension served as an analytical signal. The analysis time did not exceed 4 min. The correlation of the experimental results of an acoustic sensor with the results obtained using the light phase-contrast microscopy and standard microbiological analysis was established. The compact biological analyzer demonstrated stability, reproducibility, and repeatability of results.

A Review of Detection of Antibiotic Residues in Food by Surface-Enhanced Raman Spectroscopy

Antibiotics, as veterinary drugs, have made extremely important contributions to disease prevention and treatment in the animal breeding industry. However, the accumulation of antibiotics in animal food due to their overuse during animal feeding is a frequent occurrence, which in turn would cause serious harm to public health when they are consumed by humans. Antibiotic residues in food have become one of the central issues in global food safety. As a safety measure, rapid and effective analytical approaches for detecting these residues must be implemented to prevent contaminated products from reaching the consumers. Traditional analytical methods, such as liquid chromatography, liquid chromatography mass spectrometry, and capillary electrophoresis, involve time-consuming sample preparation and complicated operation and require expensive instrumentation. By comparison, surface-enhanced Raman spectroscopy (SERS) has excellent sensitivity and remarkably enhanced target recognition. Thus, SERS has become a promising alternative analytical method for detecting antibiotic residues, as it can provide an ultrasensitive fingerprint spectrum for the rapid and noninvasive detection of trace analytes. In this study, we comprehensively review the recent progress and advances that have been achieved in the use of SERS in antibiotic residue detection. We introduce and discuss the basic principles of SERS. We then present the prospects and challenges in the use of SERS in the detection of antibiotics in food. Finally, we summarize and discuss the current problems and future trends in the detection of antibiotics in food.

Aptamer Self-Assembly-Functionalized Nanochannels for Sensitive and Precise Detection of Chloramphenicol

Sensitive and precise determination of chloramphenicol (CAP) is of great significance for human health due to its high risk in trace amounts. Solid-state artificial nanochannels are expected to be highly promising sensing devices owing to single-molecule sensitivity, target-specific selectivity, and portability. Herein, we report an aptamer self-assembly-functionalized artificial nanochannel-based sensor for highly sensitive and precise determination of CAP. Aptamer self-assembly (AAs) served as the specific recognition component and were in situ grown on the surface of stable anodic aluminum oxide (AAO) nanochannels to develop an AAs@AAO nanochannel-based sensor. Selective interaction with CAP led to the disassembly of AAs and sensitive current change of AAs@AAO nanochannels, allowing sensitive and precise sensing of CAP in complex food samples. The developed AAs@AAO nanochannel-based sensor showed a wide linear range from 0.32 to 1600 pg. mL^-1, low limit of detection (LOD) of 0.1 pg. mL^-1, high precision with relative standard deviation of 2.9%, and quantitative recoveries of 93.4-102.2% for CAP in milk, milk powder, and honey samples. This work proposes a versatile nanochannel-based platform for facile, sensitive, and precise sensing of hazardous residues in food samples.

Rapid and sensitive detection of rotavirus by surface-enhanced Raman scattering immunochromatography

A surface-enhanced Raman scattering (SERS) immunochromatographic assay (ICA) has been developed for rapid, ultrasensitive, and quantitative detection of rotavirus in feces using double Raman molecule-labeled Au-core Ag-shell nanoparticles. The Raman signals are generated by 5,5'-dithiobis-(2-nitrobenzoic acid) and the intensity of the characteristic peak at 1334^-1 cm was detected as the analytical signal. The Raman signals were enhanced by the SERS-enhanced effect of both Au and Ag, the large amount of Raman molecules, and the hot-spot effect in the narrow gap between the Au core and Ag shell. The SERS ICA can quantitatively detect rotavirus in a concentration range of 8- 40,000 pg/mL, with detection limits of 80 pg/mL and 8 pg/mL based on naked eye observation and SERS signal detection, respectively. No cross-reaction was observed from other common pathogens. The standard deviation of the intra- and inter-batch repetitive tests is less than 10%, and the coincidence between SERS ICA and RT-qPCR as well as commercial colloidal gold ICA is 100%. The results indicated that this SERS ICA is able to quantitatively detect rotavirus in feces in 20 min with high sensitivity, selectivity, reproducibility, and accuracy and might be a promising method for the early detection of rotavirus in clinical analysis.

Detection of chloramphenicol with an aptamer-based colorimetric assay: critical evaluation of specific and unspecific binding of analyte molecules

A chloramphenicol (CAP)-binding aptamer of 80 nucleotides (nt) was reported in 2011. In 2014, it was truncated to 40 nt and has since been used by most researchers, although a careful binding study is still lacking. In this work, binding assays using isothermal titration calorimetry and various DNA-staining dyes were performed. By comparing the truncated aptamer with three control sequences, no specific binding of CAP was observed in each case. The secondary structures of the original and truncated aptamers were analyzed, and it was shown that the likelihood of the truncated aptamer to retain the same binding mechanism as the original sequence is low. We further examined gold nanoparticle (AuNP)-based label-free colorimetric assays. By quantifying the extinction ratio at 620 nm over that at 520 nm, a similar color response was observed regardless of the sequence of DNA, suggesting the color change mainly reflected other events such as the adsorption of CAP by the AuNPs, instead of aptamer binding to CAP. Salt-induced aggregation experiments suggested direct adsorption of CAP on AuNPs. CAP only weakly inhibited DNA adsorption by AuNPs but did not displace pre-adsorbed DNA. Therefore, CAP adsorption by AuNPs needs to be considered when designing related sensors, for example, by using non-aptamer sequences as controls. This work calls for careful confirmation of aptamer binding and control experiments for designing aptamer and AuNP-based biosensors.

The Growing Interest in Development of Innovative Optical Aptasensors for the Detection of Antimicrobial Residues in Food Products

The presence of antimicrobial residues in food-producing animals can lead to harmful effects on the consumer (e.g., allergies, antimicrobial resistance, toxicological effects) and cause issues in food transformation (i.e., cheese, yogurts production). Therefore, to control antimicrobial residues in food products of animal origin, screening methods are of utmost importance. Microbiological and immunological methods (e.g., ELISA, dipsticks) are conventional screening methods. Biosensors are an innovative solution for the development of more performant screening methods. Among the different kinds of biosensing elements (e.g., antibodies, aptamers, molecularly imprinted polymers (MIP), enzymes), aptamers for targeting antimicrobial residues are in continuous development since 2000. Therefore, this review has highlighted recent advances in the development of aptasensors, which present multiple advantages over immunosensors. Most of the aptasensors described in the literature for the detection of antimicrobial residues in animal-derived food products are either optical or electrochemical sensors. In this review, I have focused on optical aptasensors and showed how nanotechnologies (nanomaterials, micro/nanofluidics, and signal amplification techniques) largely contribute to the improvement of their performance (sensitivity, specificity, miniaturization, portability). Finally, I have explored different techniques to develop multiplex screening methods. Multiplex screening methods are necessary for the wide spectrum detection of antimicrobials authorized for animal treatment (i.e., having maximum residue limits).

Core-Shell Gold/Silver Nanoparticles for Localized Surface Plasmon Resonance-Based Naked-Eye Toxin Biosensing

The localized surface plasmon resonance (LSPR) phenomenon provides a versatile property for biodetection. Herein, this unique feature was employed to build a homogeneous optical biosensor to detect staphylococcal enterotoxin A (SEA) in solution down to very low levels by naked-eye readout. If the initial position of the LSPR band is located in the cyan region, even a small red shift (∼2-3 nm) induced by a refractive index change close to the surface of nanoparticles (NPs) could make the light absorption transit from cyan to green and become visually detectable via a concomitant change in the complementary colors. In this work, we aimed at synthesizing two types of NPs based on compositionally complex core-shell NPs-Ag shells on AuNPs (Au@AgNPs) and Ag inside gold nanoshells (Ag@AuNPs). By controlling the thickness of the shells and their surface chemistry with anti-SEA antibody (Ab), the LSPR band was tuned to near 495 and 520 nm for Ag@AuNPs and Au@AgNPs, respectively. The two particle systems were subsequently applied to spectroscopically and visually detect anti-SEA Ab-SEA interactions. Upon the addition of SEA, large red shifts of the LSPR band were observed spectroscopically and the limits of detection (LODs) were estimated to be 0.2 and 0.4 nM for Au@AgNPs and Ag@AuNPs, respectively. Although the two sets of NPs gave almost identical LODs, the Ag@AuNPs whose initial position of the LSPR band was tuned in the cyan to green region (∼500 nm) displayed a substantially more distinct color change from orange to red, as revealed by the naked eye. We foresee significant potential to this strategy in medical diagnostics and environmental monitoring, especially when basic laboratory infrastructure is sparse or nonexistent.

A fluorescence polarization aptasensor coupled with polymerase chain reaction and streptavidin for chloramphenicol detection

The authors describe a fluorescence polarization (FP) aptasensor based on the polymerase chain reaction (PCR) and streptavidin as dual FP amplifiers to detect chloramphenicol residues in food. Briefly, label-free aptamer was incubated with chloramphenicol and the aptamer-chloramphenicol conjugate was used as a template. Subsequently, the FAM-labeled forward primer and biotin-labeled reverse primer were added for PCR to amplify the template and the FAM-labeled primer. The molecular weight of FAM-labeled primer increased rapidly and the corresponding FP also enhanced. Finally, with the introduction of streptavidin, the PCR products and streptavidin were combined with the biotin-streptavidin interactions, resulting in much larger molecular weight. Thus, a dual amplified FP signal was obtained. Under optimal conditions, we were able to achieve a wide linear detection range of 0.001-200 nM. In addition, the designed strategy was applied to detect chloramphenicol in honey samples with high accuracy. Moreover, the strategy can be easily extended to detect other small molecules by changing the corresponding aptamers, which provide a promising avenue for the detection of small molecules by FP.

Monitoring 2,3',5,5'-tetrachlorobiphenyl with a rapid and sensitive environmental aptamer sensor

Polychlorinated biphenyl (PCB) detection in the environment is significant for both environmental protection and human health. Herein, a highly sensitive aptamer sensor has been established by employing a 2,3',5,5'-tetrachlorobiphenyl (PCB72) targeting aptamer as a highly specific recognition element and a gold/silver (Au@Ag) nanocomposite as the surface-enhanced Raman spectroscopy (SERS) substrate for detecting environmental PCB72. The Au@Ag nanoparticles (NPs) exhibit a strong SERS enhancement and provide an efficient substrate for immobilizing the PCB72 aptamer and Raman signal labelled molecule, 4-mercaptobenzoic acid (4-MBA). The targeted PCB72 could competitively bind with the PCB72 aptamer, resulting in a few aptamers sticking to the Au@Ag NPs and the "hot spot" strengthening effect of the substrate. Under optimal conditions, this aptamer sensor exhibits great performance with high sensitivity, excellent selectivity and stability for the monitoring of PCB72, which shows an excellent linear correlation ranging from 1 to 1000 pg mL-1 with a limit of detection of 0.3 pg mL-1. Furthermore, this aptamer assay exhibits high specificity and selectivity for PCB72 with the detection error of less than 0.27 for other PCBs and 0.21 for other interfering species, even if the coexisting interferents are 100-fold concentration in the system. Additionally, the recognition mechanism of the binding of aptamers to PCB72 is analyzed via UV-vis spectroscopy and molecular docking simulations, which suggest that PCB72 could insert into the aptamers. Furthermore, this method is successfully utilized for PCB72 detection in real water samples with a simple pre-treatment. In general, this work provides a new and effective method using an environmental aptamer sensor for rapid and sensitive PCB72 detection.

Quantitative and specific detection of cancer-related microRNAs in living cells using surface-enhanced Raman scattering imaging based on hairpin DNA-functionalized gold nanocages

A highly sensitive surface-enhanced Raman scattering (SERS) strategy based on hairpin DNA-functionalized gold nanocages for the detection of intracellular miR-125a-5p.

Aptasensors as the future of antibiotics test kits-a case study of the aptamer application in the chloramphenicol detection

Antibiotics are a type of antimicrobial drug with the ubiquitous presence in foodstuff that effectively applied to treat the diseases and promote the animal growth worldwide. Chloramphenicol as one of the antibiotics with the broad action spectrum against Gram-positive and Gram-negative bacteria is widely applied for the effective treatment of infectious diseases in humans and animals. Unfortunately, the serious side effects of chloramphenicol, such as aplastic anemia, kidney damage, nausea, and diarrhea restrict its application in foodstuff and biomedical fields. Development of the sufficiently sensitive methods to detect chloramphenicol residues in food and clinical diagnosis seems to be an essential demand. Biosensors have been introduced as the promising tools to overcome the requirement. As one of the newest types of the biosensors, aptamer-based biosensors (aptasensors) are the efficient sensing platforms for the chloramphenicol monitoring. In the present review, we summarize the recent achievements of the accessible aptasensors for qualitative detection and quantitative determination of chloramphenicol as a candidate of the antibiotics. The present chloramphenicol aptasensors can be classified in two main optical and electrochemical categories. Also, the other formats of the aptasensing assays like the high performance liquid chromatography (HPLC) and microchip electrophoresis (MCE) have been reviewed. The enormous interest in utilizing the diverse nanomaterials is also highlighted in the fabrication of the chloramphenicol aptasensors. Finally, some results are presented based on the advantages and disadvantages of the studied aptasensors to achieve a promising perspective for designing the novel antibiotics test kits.

Synthesis of Au@Ag core-shell nanostructures with a poly(3,4-dihydroxy-L-phenylalanine) interlayer for surface-enhanced Raman scattering imaging of epithelial cells

Poly(3,4-dihydroxy-L-phenylalanine) (polyDOPA) is a stable and biocompatible reducing agent. A versatile strategy is described here for the synthesis of core-shell Au@Ag nanostructures containing a polyDOPA interlayer. The latter provides abundant sites for deposition of nanocomposites, to immobilize molecules and to grow shells. The Au@polyDOPA@Ag nanoparticles are shown to generate strong and stable surface-enhanced Raman spectroscopy (SERS) signals compared to bare AuNPs and bare AgNPs. Folic acid was then immobilized on Au@polyDOPA@Ag nanoparticles and then applied to SERS imaging of human lung adenocarcinoma cell line A549 by the specific recognition of the folic acid receptor. The folic acid-conjugated SERS tags were promising to be nanoplatforms for imaging of cancer cells. Graphical abstract An Au@Ag core-shell nanostructures SERS nanotag with a polyDOPA interlayer was fabricated and then applied to SERS imaging of epithelial cells. (DOPA: 3,4-Dihydroxy-[_L-phenylalanine]; FA: folic acid; 4-MBA: 4-mercaptobenzoic acid).

Quantitative and Sensitive Detection of Chloramphenicol by Surface-Enhanced Raman Scattering

We used surface-enhanced Raman scattering (SERS) for the quantitative and sensitive detection of chloramphenicol (CAP). Using 30 nm colloidal Au nanoparticles (NPs), a low detection limit for CAP of 10⁻⁸ M was obtained. The characteristic Raman peak of CAP centered at 1344 cm⁻¹ was used for the rapid quantitative detection of CAP in three different types of CAP eye drops, and the accuracy of the measurement result was verified by high-performance liquid chromatography (HPLC). The experimental results reveal that the SERS technique based on colloidal Au NPs is accurate and sensitive, and can be used for the rapid detection of various antibiotics.

Ultrasensitive SERS aptasensor for the detection of oxytetracycline based on a gold-enhanced nano-assembly

This paper investigated a new detection method of oxytetracycline (OTC) in aquatic products with ultrasensitive detection limit. The method was constructed on the basis of raman hot spot between gold nanoparticles (AuNPs) (13nm and 80nm diameter respectively) linked by an DNA sequence. The DNA sequence combined with the OTC aptamer including its complementary sequence as well as a stem-loop structure. The raman signal molecule (4-MBA) was modified at the surface of 13nm AuNPs. After the exposure of OTC, the aptamer sequence was preferentially combined with OTC and partially dehybridized with its complementary sequence which led the 13nm AuNPs to get more closer to the 80nm AuNPs. The raman intensity was thus increased for the more enhanced hot spot generated. Under the optimal experimental conditions, the SERS signal was positively related to the OTC concentration with a wide working range of 4.60×10^-2-4.60×10²fg/mL and the limit of detection (LOD) was as low as 4.35×10^-3fg/mL. The recovery rates of fishmeal ranged from 91.29-110.98%. The specificity of this method was further examined, and the results showed that the AuNPs based aptasensor was highly selective. This developed ultrasensitive aptamer-based SERS detection platform suggested that it may be a promising strategy for a variety of sensing applications.

Nanoshell-Enhanced Raman Spectroscopy on a Microplate for Staphylococcal Enterotoxin B Sensing

A sensitive surface-enhanced Raman scattering (SERS) immunosensor based on the Au nanoparticle (Au NP) shell structure was developed to detect staphylococcal enterotoxin B (SEB) on a microplate. Au NPs modified with 4-nitrothiophenol (4-NTP) and coated with Ag shell of controlled thickness at 6.6 nm exhibited excellent SERS intensity and were used as signal reporters in the detection of SEB. The engaged 4-NTP allowed the significant electromagnetic enhancement between Au NPs and the Ag shell and prevented the dissociation of the Raman reporter. More importantly, 4-NTP-differentiated SERS signals between the sample and microplate. The SERS-based immunosensor had a limit of detection of 1.3 pg/mL SEB. Analysis of SEB-spiked milk samples revealed that the developed method had high accuracy. Therefore, the SERS-encoded Au@Ag core-shell structure-based immunosensor is promising for the detection of biotoxins, pathogens, and environmental pollutants.

Hybridized enhancement of the SERS detection of chemical and bio-marker molecules through Au nanosphere ornamentation of hybrid amorphous/crystalline Si nanoweb nanostructure biochip devices

We report the fabrication of hybrid Si SERS nanobiosensor biochip devices.