A novel colorimetric aptasensor for detection of chloramphenicol based on lanthanum ion-assisted gold nanoparticle aggregation and smartphone imaging

Optical detection based spot test on electrospun nanofibers for glioblastoma cells

Paper-based diagnosis is enabled to be used in many applications in global health due to its low cost and simplicity of operation. Electrospun nanofibers (ESNFs) are useful platforms to prepare paper-based diagnostics. Herein, bead-free ESNFs were formed by electrospinning using polystyrene (PS) and poly (ethylene glycol) (PEG) polymers as a paper-based substrate. PS:PEG ESNFs were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), identification of swelling behavior, and Brunauer-Emmett-Teller (BET) analysis. Synthesized gold nanoparticles (AuNPs) were used as a colorimetric probe and GMT8 aptamer was conjugated on the surface of AuNPs. AuNP and AuNP-GMT8 were characterized by dynamic light scattering (DLS), UV-Visible spectrometry, and X-Ray photoelectron spectroscopy (XPS). The interaction of AuNP-GMT8 bioconjugates with glioblastoma cells was examined. The colored spots for the mixture of glioblastoma (U87-MG) cells and AuNP-GMT8 were optically monitored both in the microplate wells and on the PS:PEG ESNFs. The linear range of colorimetric analysis on PS:PEG ESNFs was determined to be between 101-106 U87-MG cells/mL by smartphone using RGB color analysis.

Detection of zearalenone in miscellaneous beans by functionalized SERS sensor based on sea urchin aptamer

In this work, a sea urchin gold nanoparticles-zearalenone aptamer- tetramethylrhodamine sensor was constructed. Sea urchin gold nanoparticles, prepared using the seed-mediated growth method, were used as Raman substrates. Nucleic acid aptamers were mainly used as specific recognition molecules. Zearalenone detection in miscellaneous beans was accomplished using the principle of conformational change in aptamer. In addition, we evaluated the linear range, sensitivity, and selectivity of our sensor. We observed that at the displacement of 814 cm-1, for Zearalenone concentrations of 0.01-60 ng/mL, the Raman signal intensity linearly correlated with the zearalenone concentration, with a limit of detection of 0.01 ng/mL, and recoveries of 91.7% to 108.3%. The optimum detection time was 30 min. Thus, our sensor exhibited great potential in zearalenone detection in food products.

Beetle-inspired AuNPs semi-embedded colloidal crystal chips for the highly sensitive and colored detection of chloramphenicol in foods

Inspired by the desert beetle, a novel biomimetic chip was developed to detect chloramphenicol (CP). The chip was characterized by a periodic array in which hydrophobic Au nanoparticles (AuNPs) were semi-embedded on hydrophilic polymethyl methacrylate (PMMA) spheres. Among them, the AuNPs exhibited both a localized surface plasmon resonance effect to amplify the reflected signal and a synergistic effect with PMMA spheres to create a significant hydrophilic-hydrophobic interface, which facilitated the enrichment of target CP molecules and improved sensitivity. After optimization, the chip showed direct, ultrasensitive (as low as 0.2 ng/mL), fast (5 min), and selective detection of CP with a wide concentration range extending from 0.2 ng/mL to 1000 ng/mL. During detection, color changes of the chip were observed by naked eyes without any color display equipment. The recovery of CP was between 94.65 % and 108.70 % in chicken and milk samples.

Smartphone-integrated visual inspection for enhancing agricultural product quality and safety: a review

The increasing emphasis on the quality and safety of agricultural products, which are vital to global trade and consumer health, has driven the innovation of cost-effective, convenient, and rapid smart detection technologies. Smartphones, with their interdisciplinary functionalities, have become valuable tools in quantification and analysis research. Acting as portable, affordable, and user-friendly analytical devices, smartphones are equipped with high-resolution cameras, displays, memory, communication modules, sensors, and operating systems (Android or IOS), making them powerful, palm-sized remote computers. This review delves into how visual inspection technology and smartphones have enhanced the quality and safety of agricultural products over the past decade. It also evaluates the key features and limitations of existing smart rapid inspection methods for agricultural products and anticipates future advancements, offering insights into the application of smart rapid inspection technology in agriculture.

Non-immobilized GO-SELEX screening of aptamers against cyclosporine A and its application in a AuNPs colorimetric aptasensor

Cyclosporine A (CsA) is an immunosuppressive drug that is widely used in clinical practice. Due to its narrow therapeutic window and the significant differences between individuals, the therapeutic drug monitoring (TDM) of CsA is required to ensure patient safety. In this study, we screened a novel aptamer, named CsA7, which could specifically recognize CsA, and developed a AuNPs colorimetric aptasensor for the rapid detection of CsA. In the SELEX process, after eight rounds of screening, four aptamer candidate sequences were obtained and subjected to binding affinity and specificity tests. Finally, the CsA7 aptamer (Kd = 41.21 ng mL-1) showed the highest affinity for CsA. Based on CsA7, we also developed a AuNPs colorimetric aptasensor, which had a detection limit of 0.1 ng mL-1 and a quantitative range of 0.1-500 ng mL-1 and showed good selectivity among CsA and its analogs. According to the results, the CsA7 aptamer provides an alternative recognition molecule to the antibody in biosensor applications and shows great potential for the rapid and convenient detection of CsA.

Lateral Flow Immunoassay Based on Quantum-Dot Nanobeads for Detection of Chloramphenicol in Aquatic Products

Quantum dot nanobeads (QBs) were used as signal source to develop competitive lateral flow immunoassay (LFIA) for the detection of chloramphenicol (CAP). The quantitative detection of CAP was achieved by calculating the total color difference (∆E) values of the test line (T line) using the images of test strips. QB-based LFIA (QBs-LFIA) allowed the effective dynamic linear detection of CAP in the range of 0.1-1.5 ng/mL. The limit of detection (LOD) was 3.0 ng/mL, which was 50 and 667 times lower than those achieved for two different brands of colloidal gold kits. The recoveries of CAP during real-sample detection were 82.82-104.91% at spiked levels of 0.1, 0.7, and 1.5 ng/mL. These results indicate that the developed QBs-LFIA facilitates the sensitive detection of CAP.

A smartphone-assisted colorimetric aptasensor based on aptamer and gold nanoparticles for visual, fast and sensitive detection of ZEN in maize

A simple, fast, low cost, sensitive, intuitive, visual, label-free, and smartphone-assisted aptamer sensor based on colorimetric assay for the measurement of zearalenone was constructed. The nucleic acid aptamer of zearalenone was used as the recognition element and gold nanoparticles were used as the indicator. Several factors that could influence sensitivity, including the concentration of aptamer and NaCl, and incubation time, and specificity, have been investigated. The results showed that under the optimal conditions, the signal had a good linear relationship when zearalenone concentration is 5-300 ng/mL. A linear regression equation is Y = 0.0003X + 0.5128 (R2 = 0.9989) and a limit of detection is 5 ng/mL. The specificity of the sensor was good. Zearalenone in maize samples were successfully measured. The recoveries of Zearalenone are 81.3 %-96.4 %. The whole process takes only 15 min to complete. The smartphone assisted colorimetric aptamer sensor can be used for the detection of zearalenone in maize.

Plasmonic nanoparticle's anti-aggregation application in sensor development for water and wastewater analysis

Colorimetric sensors have emerged as a powerful tool in the detection of water pollutants. Plasmonic nanoparticles use localized surface plasmon resonance (LSPR)-based colorimetric sensing. LSPR-based sensing can be accomplished through different strategies such as etching, growth, aggregation, and anti-aggregation. Based on these strategies, various sensors have been developed. This review focuses on the newly developed anti-aggregation-based strategy of plasmonic nanoparticles. Sensors based on this strategy have attracted increasing interest because of their exciting properties of high sensitivity, selectivity, and applicability. This review highlights LSPR-based anti-aggregation sensors, their classification, and role of plasmonic nanoparticles in these sensors for the detection of water pollutants. The anti-aggregation based sensing of major water pollutants such as heavy metal ions, anions, and small organic molecules has been summarized herein. This review also provides some personal insights into current challenges associated with anti-aggregation strategy of LSPR-based colorimetric sensors and proposes future research directions.

Rational Truncation of Aptamer for Ultrasensitive Aptasensing of Chloramphenicol: Studies Using Bio-Layer Interferometry

Aptamers are an excellent choice for the selective detection of small molecules. However, the previously reported aptamer for chloramphenicol suffers from low affinity, probably as a result of steric hindrance due to its bulky nature (80 nucleotides) leading to lower sensitivity in analytical assays. The present work was aimed at improving this binding affinity by truncating the aptamer without compromising its stability and three-dimensional folding. Shorter aptamer sequences were designed by systematically removing bases from each or both ends of the original aptamer. Thermodynamic factors were evaluated computationally to provide insight into the stability and folding patterns of the modified aptamers. Binding affinities were evaluated using bio-layer interferometry. Among the eleven sequences generated, one aptamer was selected based on its low dissociation constant, length, and regression of model fitting with association and dissociation curves. The dissociation constant could be lowered by 86.93% by truncating 30 bases from the 3' end of the previously reported aptamer. The selected aptamer was used for the detection of chloramphenicol in honey samples, based on a visible color change upon the aggregation of gold nanospheres caused by aptamer desorption. The detection limit could be reduced 32.87 times (1.673 pg mL^-1) using the modified length aptamer, indicating its improved affinity as well as its suitability in real-sample analysis for the ultrasensitive detection of chloramphenicol.

AFB1 colorimetric aptamer sensor for the detection of AFB1 in ten different kinds of miscellaneous beans based on gold nanoparticles and smartphone imaging

A simple, rapid, low-cost, sensitive, intuitive, visual, label-free, colorimetric smartphone-assisted assay was developed for the measurement of aflatoxin B1 in miscellaneous beans. Ten different kinds of miscellaneous beans were treated and measured by modified QuEChERS(Quick、Easy、Cheap、Effective、Rugged、Safe) method with aflatoxin B1 nucleic acid aptamer as a recognition element and gold nanoparticles as indicators. Several factors influencing its sensitivity were investigated, including consumes and NaCl concentrations, as well as incubation time and specificity. The results showed a good linear relationship between concentrations of 0.2-8.0 ng/g under optimal conditions. With a detection limit of 0.08 ng/g, the linear regression equation was Y = 0.024X + 0.4615 (R = 0.9989). Sensor specificity is good. The content of aflatoxin B1 in bean samples was determined successfully. The recovery of aflatoxin B1 ranged from 87.18% to 110.24%. The whole thing took 15 min. This smartphone-assisted colorimetric aptamer sensor can be used to detect aflatoxin B1 in beans.

Metrological traceability in process analytical technologies and point-of-need technologies for food safety and quality control: not a straightforward issue

Traditional techniques for food analysis are based on off-line laboratory methods that are expensive and time-consuming and often require qualified personnel. Despite the high standards of accuracy and metrological traceability, these well-established methods do not facilitate real-time process monitoring and timely on-site decision-making as required for food safety and quality control. The future of food testing includes rapid, cost-effective, portable, and simple methods for both qualitative screening and quantification of food contaminants, as well as continuous, real-time measurement in production lines. Process automatization through process analytical technologies (PAT) is an increasing trend in the food industry as a way to achieve improved product quality, safety, and consistency, reduced production cycle times, minimal product waste or reworks, and the possibility for real-time product release. Novel methods of analysis for point-of-need (PON) screening could greatly improve food testing by allowing non-experts, such as consumers, to test in situ food products using portable instruments, smartphones, or even visual naked-eye inspections, or farmers and small producers to monitor products in the field. This requires the attention of the research community and devices manufacturers to ensure reliability of measurement results from PAT strategy and PON tests through the demonstration and critical evaluation of performance characteristics. The fitness for purpose of methods in real-life conditions is a priority that should not be overlooked in order to maintain an effective and harmonized food safety policy.

Applications of Smartphone-Based Aptasensor for Diverse Targets Detection

Aptamers are a particular class of functional recognition ligands with high specificity and affinity to their targets. As the candidate recognition layer of biosensors, aptamers can be used to sense biomolecules. Aptasensors, aptamer-based biosensors, have been demonstrated to be specific, sensitive, and cost-effective. Furthermore, smartphone-based devices have shown their advantages in binding to aptasensors for point-of-care testing (POCT), which offers an immediate or spontaneous responding time for biological testing. This review describes smartphone-based aptasensors to detect various targets such as metal ions, nucleic acids, proteins, and cells. Additionally, the focus is also on aptasensors-related technologies and configurations.

Plasma colorimetric aptasensor for the detection of chloramphenicol in honey based on cage Au@AuNPs and cascade hybridization chain reaction

A plasma colorimetric aptasensor was developed for rapid determination of chloramphenicol (CAP) in honey on site. Herein, cage gold shell@core nanoparticles (Au@AuNPs) were synthesized to enhance signal response and broaden the linear range. In addition, aptamer-based cascade hybridization chain reaction (cHCR), consisting of HP1, HP2, HP3, and HP4, was also designed for signal amplification and specific analysis. In this assay, HP1 and HP4 were immobilized on the surface of cage Au@AuNPs. In the presence of CAP, cHCR was triggered, and frond-like DNA products were formed, which made the distance among the cage Au@AuNPs closer and the system color changed from red to deep purple. Qualitative and quantitative analysis were carried out according to color changes and UV-Vis spectra. Under the optimized conditions, the wavelength of UV-Vis absorption peak exhibited a good linear relationship with CAP concentration in the range of 5.0 to 500 nmol/L with the detection limit of 1.2 nmol/L (S/N = 3). This aptasensor also showed good specificity for CAP detection compared with other antibiotics similar to the target analyte. Furthermore, the colorimetric aptasensor was successfully applied to the detection of CAP in honey with recoveries of 88.0-107.6%. This cHCR-based aptasensing for CAP possesses high sensitivity, good selectivity, low cost and excellent stability, and could be extended to detect a wide variety of other small molecular analytes, nucleic acids or proteins. Therefore, the versatile method might become a potential alternative tool in food analysis and environmental monitoring.

A simple and sensitive AuNPs-based colorimetric aptasensor for specific detection of azlocillin

A new colorimetric biosensor for specific detection of azlocillin was developed by using DNA aptamer as recognition element and unmodified gold nanoparticles (AuNPs) as colorimetric indicator. In the absence of azlocillin, the AuNPs were protected by the aptamer and stabilized at high NaCl concentrations, displaying a red solution. In the presence of azlocillin, the aptamer reacts specifically with azlocillin, resulting in the aggregation of AuNPs and an apparent red to blue color change. The characteristic change can be easily observed by the naked eye and quantitatively detected by an ultraviolet-visible (UV-Vis) spectrometer. Under the optimal conditions, the absorbance variation at 522 nm (ΔA₅₂₂) of AuNPs changed proportionally with increasing concentration of azlocillin, which exhibited a linear relationship in the concentration range of 50 nM to 500 nM, with a detection limit of 11.6 nM. Furthermore, the aptasensor was successfully used to detect azlocillin in milk and tap water samples, with recoveries ranging from 97.64% to 102.21% and a relative standard deviation (RSD) less than 3.81%.

Bio-Receptors Functionalized Nanoparticles: A Resourceful Sensing and Colorimetric Detection Tool for Pathogenic Bacteria and Microbial Biomolecules

Pathogenic bacteria and several biomolecules produced by cells and living organisms are common biological components posing a harmful threat to global health. Several studies have devised methods for the detection of varying pathogenic bacteria and biomolecules in different settings such as food, water, soil, among others. Some of the detection studies highlighting target pathogenic bacteria and biomolecules, mechanisms of detection, colorimetric outputs, and detection limits have been summarized in this review. In the last 2 decades, studies have harnessed various nanotechnology-based methods for the detection of pathogenic bacteria and biomolecules with much attention on functionalization techniques. This review considers the detection mechanisms, colorimetric prowess of bio-receptors and compares the reported detection efficiency for some bio-receptor functionalized nanoparticles. Some studies reported visual, rapid, and high-intensity colorimetric detection of pathogenic bacteria and biomolecules at a very low concentration of the analyte. Other studies reported slight colorimetric detection only with a large concentration of an analyte. The effectiveness of bio-receptor functionalized nanoparticles as detection component varies depending on their selectivity, specificity, and the binding interaction exhibited by nanoparticles, bio-receptor, and analytes to form a bio-sensing complex. It is however important to note that the colorimetric properties of some bio-receptor functionalized nanoparticles have shown strong and brilliant potential for real-time and visual-aided diagnostic results, not only to assess food and water quality but also for environmental monitoring of pathogenic bacteria and a wide array of biomolecules.

Aptasensor: Surface protein detection in case of coronavirus diagnosis

Coronavirus disease (COVID-19) pandemic has left a disastrous effect on the world wealth and human evolution. The recent outbreak of COVID-19 disease is an infectious disease caused by newly discovered severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) which belongs to the single-stranded, positive strand RNA viruses. SARS‑CoV‑2 are dangerous threat to public health, economics, and global disciples. Therefore, it is important to identify, isolate, and treat individuals at the early stages of the disease to control the spread. In the present scenario, various analytical tools are available for the detection of several kinds of viruses through the use of different types of biosensing technologies. During the last decades, biosensors have emerged as reliable analytical devices and provide new promising tool for the detection of viruses. Aptamers are ssDNA or RNA oligonucleosides selected by the technique of systematic evolution of ligands by exponential enrichment (SELEX). Aptamers can bind various targets from small molecules to cells or even tissues in the way of antibodies. Aptameric nanobiosensors are rapid and sensitive diagnostic platforms, capable of SARS-CoV-2 detection, which overcomes the limitations of the conventional techniques. This chapter presents the use of aptamers in the fabrication of biosensors for improved diagnosis of SARS-CoV-2 and the future perspectives are also discussed.

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 selective detection of aluminum ion using 1,2,3-triazole-4,5-dicarboxylic acid-functionalized gold nanoparticle-based colorimetric sensor

A highly selective, sensitive, rapid, low-cost, simple and visual colorimetric system for Al3+ ion detection was developed based on gold nanoparticles (AuNPs) modified with 1,2,3-triazole-4,5-dicarboxylic acid (TADA). The modified gold nanoparticles (TADA-AuNPs) were first prepared by sodium citrate (Na3Ct) reduction of chloroauric acid (HAuCl4) and then capped with a TADA ligand. Five TADA-AuNPs sensors were constructed with sodium citrate (Na3Ct)/chloroauric acid (HAuCl4) under different molar ratios. Results showed that the molar ratio of Na3Ct/HAuCl4, TADA-AuNPs concentration, pH range and detection time had obvious influences on the performance of this colorimetric method. The optimal detection conditions for Al3+ ions were as follows: Na3Ct/HAuCl4 molar ratio of 6.4 : 1, 0.1 mM of TADA-AuNPs concentration, 4-10 pH range and 90 s of detection time. Under the optimal conditions and using diphenyl carbazone (DPC) as a Cr3+ masking agent, this colorimetric sensor exhibited outstanding time efficiency, selectivity and sensitivity for Al3+ detection. In particular, the detection limits of this sensor obtained via UV-vis and the naked eye were 15 nM and 1.5 μM, respectively, which were much lower than the current limit (3.7 μM) for drinking water in WHO regulation and better than the previous reports. Moreover, this colorimetric sensing system could be used to for on-site, trace level and real-time rapid detection of Al3+ in real water samples.

Recent progress in smartphone-based techniques for food safety and the detection of heavy metal ions in environmental water

Emerging smartphone-based point-of-care tests (POCTs) are cost-effective, precise, and easy to implement in resource-limited areas. Thus, they are considered a potential alternative to conventional diagnostic testing. This review explores food safety and the detection of metal ions in environmental water based on unprecedented smartphone technology. Specifically, we provide an overview of various methods used for target analyte detection (antibiotics, enzymes, mycotoxins, pathogens, pesticides, small molecules, and metal ions), such as colorimetric, fluorescence, microscopic imaging, and electrochemical methods. This paper performs a comprehensive review of smartphone-based POCTs developed in the last three years (2018-2020) and evaluates their relative advantages and limitations. Moreover, we discuss the imperative role of new technology in the progress of POCTs. Sensor materials (metal nanoparticles, carbon dots, quantum dots, organic substrates, etc.) and detection techniques (paper-based, later flow assay, microfluidic platform, etc.) involved in POCTs based on smartphones, and the challenges faced by these techniques, are addressed.

Rapid visual detection for nitroreductase based on the copper ions-induced and NADH-mediated aggregation of gold-silver alloy nanoparticles

Hypoxia refers to the lack of oxygen supply to cells or tissues. The overexpression of nitroreductase has been shown to be closely related to the degree of hypoxia, which leads to the level of nitroreductase (NTR) being used as an indicator of hypoxia. We reported a facile visual detection of NTR based on the aggregation of gold and silver alloy nanoparticles. Compared with gold nanoparticles (AuNPs), the aggregation behavior of Au₈₀Ag₂₀ NPs caused a more prominent color change. Copper ions (Cu²⁺) can be rapidly reduced by nicotinamide adenine dinucleotide (NADH) under the catalysis of Au₈₀Ag₂₀ NPs. But NADH is consumed as an electron donor during the catalytic reduction reaction of p-nitrophenol (pNP) by NTR. A decrease of NADH amount results in the aggregation of Au₈₀Ag₂₀ NPs by the excess Cu²⁺ and different aggregation degrees of Au₈₀Ag₂₀ NPs lead to observable color change. A linear correlation of A₆₀₀/A₅₀₅ = 0.0285 [NTR]+0.361 (R² = 0.980) was obtained with a limit of detection (LOD) of 0.23 μg/mL for UV-vis spectrophotometer. For visual detection, the values of R/B against the concentration of NTR obtains a calibration curve of R/B = -0.031 [NTR]+ 1.54 (R² = 0.985) with a LOD of 0.76 μg/mL, which is of the same order of magnitude as the UV-vis spectrophotometer analysis. As a comparison, Au₈₀Ag₂₀ NPs was replaced by several different composition nanoparticles (Au NPs, Au₇₀Ag₃₀ NPs, Au₅₀Ag₅₀ NPs) to be a chromogenic substrate, and the results suggest the Au₈₀Ag₂₀ NPs is the most sensitive substrate in our assay. Selectivity tests showed that the detection system did not respond to other common substances, and the reaction mechanism was verified by inhibitor research. Finally, the assay was used on the human serum samples with spiking NTR, and the recovery rates of this assay with UV-vis spectrophotometer were basically consistent with RGB analysis.

ASSURED Point-of-Need Food Safety Screening: A Critical Assessment of Portable Food Analyzers

Standard methods for chemical food safety testing in official laboratories rely largely on liquid or gas chromatography coupled with mass spectrometry. Although these methods are considered the gold standard for quantitative confirmatory analysis, they require sampling, transferring the samples to a central laboratory to be tested by highly trained personnel, and the use of expensive equipment. Therefore, there is an increasing demand for portable and handheld devices to provide rapid, efficient, and on-site screening of food contaminants. Recent technological advancements in the field include smartphone-based, microfluidic chip-based, and paper-based devices integrated with electrochemical and optical biosensing platforms. Furthermore, the potential application of portable mass spectrometers in food testing might bring the confirmatory analysis from the laboratory to the field in the future. Although such systems open new promising possibilities for portable food testing, few of these devices are commercially available. To understand why barriers remain, portable food analyzers reported in the literature over the last ten years were reviewed. To this end, the analytical performance of these devices and the extent they match the World Health Organization benchmark for diagnostic tests, i.e., the Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, and Deliverable to end-users (ASSURED) criteria, was evaluated critically. A five-star scoring system was used to assess their potential to be implemented as food safety testing systems. The main findings highlight the need for concentrated efforts towards combining the best features of different technologies, to bridge technological gaps and meet commercialization requirements.

A novel smartphone-based colorimetric aptasensor for on-site detection of Escherichia coli O157:H7 in milk

Effective testing tools for Escherichia coli O157:H7 can prevent outbreaks of foodborne illness. In this paper, a smartphone-based colorimetric aptasensor was developed using functionalized gold nanoparticles (GNP) and multi-walled carbon nanotubes (MWCNT) for monitoring E. coli O157:H7 in milk. The maximum absorption peak of GNP bonded with aptamer (Apt) generated evident transformation from 518 to 524 nm. The excess GNP-Apt was removed by functionalized MWCNT magnetized with carbonyl iron powder (CIP) and hybridized with a DNA probe, whereas the GNP-Apt immobilized on E. coli O157:H7 remained in the system. In the presence of a high-salt solution, the GNP-Apt that captured E. coli O157:H7 remained red, but the free GNP-Apt aggregated and appeared blue. The chromogenic results were analyzed by a smartphone-based colorimetric device that was fabricated using acrylic plates, a light-emitting diode, and a mobile power pack. To our knowledge, this was the first attempt to use a smartphone-based colorimetric aptasensor employing the capture of GNP-Apt coupled with separation of MWCNT@CIP probe to detect E. coli O157:H7. The aptasensor exhibited good reproducibility and no cross-reaction for other bacteria. A concentration of 8.43 × 10³ cfu/mL of E. coli O157:H7 could be tested in pure culture, and 5.24 × 10² cfu/mL of E. coli O157:H7 could be detected in artificially contaminated milk after 1 h of incubation. Therefore, the smartphone-based colorimetric aptasensor was an efficient tool for the detection of E. coli O157:H7 in milk.

Aptamers: The Powerful Molecular Tools for Virus Detection

Aptamers are short single-stranded DNA or RNA oligonucleotides selected by the technique of systematic evolution of ligands by exponential enrichment (SELEX). Aptamers have been demonstrated to bind various targets from small-molecule to cells or even tissues in the way of antibodies. Thus, they are called chemical antibodies. We summarize and evaluate recent developments in aptamer-based sensors (for short aptasensors) for virus detection in this review. These aptasensors are mainly classified into optical and electronic aptasensors based on the type of transducer. Nowadays, the smartphone has become the most widely used mobile device with billions of users worldwide. Considering the ongoing COVID-19 outbreak, smartphone-based aptasensors for a portable and point-of-care test (POCT) of COVID-19 detection will be of great importance in the future.

Advances in Gold Nanoparticles-Based Colorimetric Aptasensors for the Detection of Antibiotics: An Overview of the Past Decade

Misuse of antibiotics has recently been considered a global issue because of its harmful effects on human health. Since conventional methods have numerous limitations, it is necessary to develop fast, simple, sensitive, and reproducible methods for the detection of antibiotics. Among numerous recently developed methods, aptasensors are fascinating because of their good specificity, sensitivity and selectivity. These kinds of biosensors combining aptamer with colorimetric applications of gold nanoparticles to recognize small molecules are becoming more popular owing to their advantageous features, for example, low cost, ease of use, on-site analysis ability using naked eye and no prerequisite for modern equipment. In this review, we have highlighted the recent advances and working principle of gold nanoparticles based colorimetric aptasensors as promising methods for antibiotics detection in different food and environmental samples (2011–2020). Furthermore, possible advantages and disadvantages have also been summarized for these methods. Finally, the recent challenges, outlook, and promising future perspectives for developing novel aptasensors are also considered.

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.

Recent Biosensors for Detection of Antibiotics in Animal Derived Food

Antibiotics are extensively employed as bacteriostatic agents for fighting against microbial infection in animals. However, inappropriate doses of antibiotic drugs may result in antibiotic residues in food of animal origin and may cause various side effects on human health. Moreover, the transferor of antibiotic-resistant bacteria to humans through the food chain may induce serious health hazards. Hence, it is vital to develop sensitive and selective methods for rapid screening and regular monitoring of antibiotic residues in animal-derived foods. The conventional different chromatographic and spectroscopic techniques are time-consuming, expensive and require skilled personnel. To overcome such limitations, biosensors have emerged as an innovative approach recently and integrated with nanotechnologies for sensitive, rapid and on-site monitoring of different antibiotic residues in animal origin foods. This mini-review aims to give an overview of the currently available biosensing techniques to detect antibiotic residue in foods.

Design and fabrication of a highly sensitive and naked-eye distinguishable colorimetric biosensor for chloramphenicol detection by using ELISA on nanofibrous membranes

Enzyme-linked immunoassay (ELISA) is highly specific and selective towards target molecules and is convenient for on-site detection. However, in many cases, lack of high sensitivity makes it hard to reveal a significant colorimetric signal for detecting a trace amount of target molecules. Thus, analytical instruments are required for detection, which limits the application of ELISA for on-site detection. In the present study, a highly sensitive and naked-eyed detectable colorimetric biosensor for chloramphenicol (CAP) was prepared by incorporating ELISA onto surfaces of microporous and nanofibrous membranes. The high specific surface areas of the nanofibers significantly increased the number of antibodies covalently linked onto the fiber surfaces and binding capacity of the sensor with antigens present in a sample. With such an integration, the sensitivity of the ELISA sensor was dramatically increased, and a trace number of targets could reveal a naked-eye detectable color. The immunoassay sensor exhibited a significant naked-eye distinguishable color to chloramphenicol (CAP) at 0.3 ng/mL. The successful design and fabrication of the nanofibrous membrane immunoassay sensor provide new paths towards the development of on-site inspection sensors without the assistance from any instrument.

Smartphone-based optical assays in the food safety field

Smartphone based devices (SBDs) have the potential to revolutionize food safety control by empowering citizens to perform screening tests. To achieve this, it is of paramount importance to understand current research efforts and identify key technology gaps. Therefore, a systematic review of optical SBDs in the food safety sector was performed. An overview of reviewed SBDs is given focusing on performance characteristics as well as image analysis procedures. The state-of-the-art on commercially available SBDs is also provided. This analysis revealed several important technology gaps, the most prominent of which are: (i) the need to reach a consensus regarding optimal image analysis, (ii) the need to assess the effect of measurement variation caused by using different smartphones and (iii) the need to standardize validation procedures to obtain robust data. Addressing these issues will drive the development of SBDs and potentially unlock their massive potential for citizen-based food control.

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Optical smartphone based sensors in the food safety field are systematically reviewed.

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Recommendations on image analysis optimization are given.

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The analytical performance of smartphone based sensors is discussed.

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Available commercial devises are critically compared.