Colorimetric Aptasensor Research Articles

Colorimetric aptasensor based on temporally controllable light-stimulated oxidase-mimicking fluorescein for the sensitive detection of exosomes in mild conditions.

Analysis of exosomes provides important information for rapid and non-invasive screening of tumors. However, sensitive and convenient detection of exosomes remains technically challenging to date. Herein, a colorimetric aptasensor based on the light-stimulated oxidase-mimicking activity of FITC was constructed for detecting ovarian cancer (OC) exosomes. The aptasensor contained an EpCAM aptamer to capture OC exosomes. Cholesterol and fluorescein (FITC) were used to modify either end of the DNA (DNA anchor). The DNA anchor could combine with exosomes through a hydrophobic reaction between cholesterol and the lipid membrane. FITC oxidized 3,3',5,5'-tetramethylbenzidine (TMB) under a 365 nm LED light source in a temporally controllable manner under mild conditions, causing the solution to change from colorless to blue, and the corresponding UV-vis absorbance increased. Based on this principle, the exosomes were qualitatively analyzed by observing the color change with the naked eye. In parallel, the exosome concentration was also detected using UV-vis spectrophotometry. The linear range was from 2 × 105 to 100 × 105 particles per mL with a limit of detection of 1.77 × 105 particles per mL. The developed aptasensor also exhibited favorable selectivity and could discriminate the exosomes from OC cells and normal cells. Besides, the receiver operating characteristic (ROC) curve demonstrates that it is possible to distinguish between patients with OC and healthy donors (HDs) using exosomes as the biomarker. Our technology may expand the applications of DNA-based detection method-enabled OC diagnostic tools.

Detection of acrylamide in food based on MIL-glucose oxidase cascade colorimetric aptasensor

BackgroundMaillard reaction involves the polymerization, condensation, and other reactions between compounds containing free amino groups and reducing sugars or carbonyl compounds during heat processing. This process endows unique flavors and colors to food, while it can also produce numerous hazards. Acrylamide (AAm) is one of Maillard's hazards with neurotoxicity and carcinogenicity, these effects can trigger mutations and alternations in gene expression in human cells and accelerate organ aging. An accurate and reliable acrylamide detection method with high sensitivity and specificity for future regulatory activities is urgently needed. ResultsHerein, we constructed a colorimetric aptasensor with the hybridization of MIL-glucose oxidase (MGzyme)-cDNA and magnetic nanoparticle-aptamer (MNP-Apt) to specifically detect AAm. The incorporation of MB-Apt and AAm released MGzyme-cDNA in the supernatant, took the supernatant out, with the addition of glucose and TMB, MGzyme would oxidize glucose, the resulting •OH facilitated the oxidation of colorless TMB to blue ox-TMB. The absorbance value at 652 nm, which indicates the characteristic absorption peak of ox-TMB, exhibited a proportion to the concentration of AAm. MGzyme avoided the addition of harmful intermediate H2O2 and created an acid microenvironment for the catalytic reaction. MNP-Apt possessed the advantages of high specificity and simplified separation. Under optimal conditions, this method displayed a linear range of 0.01–100 μM with the limit of detection of 1.53 nM. With the spiked analysis data cross-verified by ELISA kit, this aptasensor was proven to specifically detect AAm at low concentrations. SignificanceThis colorimetric aptasensor was the integration of aptamer and the enzyme-cascade system, which could broaden the applicable range of enzyme-cascade system, break the limits of specific detection of substrates, eliminate the need for harmful intermediates, improve the reaction efficiency, implement the specific detection, whilst enabling the accurate detection of AAm. Given these remarkable performances, this method has shown significant potential in the field of food safety inspection.

Devising a colorimetric aptasensor for detection of basal stem rot-associated RNA marker during early Ganoderma boninense infection in oil palm

Basal stem rot (BSR) is a detrimental disease in oil palm (Elaeis guineensis) due to the host's lack of symptoms during the early phase of infection. Early detection of BSR at non-symptomatic phase is feasible via molecular-based approaches and has become the major interest among researchers. Our previous study had identified a differentially expressed gene encoding auxin efflux carrier component 5-like (EgPIN5) at 11 day-post-inculation of Ganoderma boninense (symptomless early stage of infection) on oil palm seedlings. We further evaluated the gene expression on samples collected from an oil palm plantation at different BSR stages (symptomless, mild and severe). Our findings revealed that EgPIN5 was expressed in symptomless group but was not expressed in either mild or severe BSR groups. Next, we developed a sandwich-type aptamer-based lateral flow assay (LFA) against EgPIN5 RNA by adapting the versatile DNA-functionalized gold nanoparticles for colorimetric detection. The LFA strip demonstrated visible colorimetric signal of EgPIN5 RNA at 12.5 ng/μL with limit of detection at 2.45 ng/μL using a scanning device. Based on our consistent results, we presented EgPIN5 as a diagnostic biomarker for symptomless BSR infection in oil palm. Utilization of LFA assay strip for practical EgPIN5 RNA detection is hoped to encourage establishment of a fast, cheap, and sensitive point-of-care detection system in plant biology.

µPAD-based colorimetric nanogold aptasensor for CRP and IL-6 detection as sepsis biomarkers

Point-of-care testing is defined as medical diagnostic testing at or near the time and place of a patient. The integration of microfluidics with functionalized nanomaterials provides a rapid and sensitive detection method for biomarkers. Due to their optical characteristics, gold nanoparticles (GNPs) and aptamers can be used in a colorimetric technique. In this research, accurate and quick aptasensors were created using aptamers for two sepsis biomarkers, interleukin-6 (IL-6) and C-reactive protein (CRP). Aptamers were combined with GNPs to create aptasensors, which were then used to analyze various biomarker concentrations after aptamer-protein docking on the online HDOCK server to verify aptamer-protein interactions. To improve the results' stability and ease of use during the reaction time, microfluidic paper-based analytical devices (µPAD) was employed. The linear diagnostic ranges in this method were 50–1000 mg L−1 and 1–25 ng/L, and limit of detection values were 1.9 mg L−1 and 0.07 ng/L for CRP and IL-6, respectively; These values decreased when µPADs were used and became more suitable to diagnosis of sepsis. Two aptasensors were highly stable, reproducible, accurate, and recoverable. Our result suggests that colorimetric GNPs can be used to detect a specific analyte through color changes visible to the naked eye for monitoring purposes or as simple optical detectors for quantitative measurements.

G-triplex/hemin DNAzyme mediated colorimetric aptasensor for Escherichia coli O157:H7 detection based on exonuclease III-assisted amplification and aptamers-functionalized magnetic beads

Escherichia coli O157: H7 (E. coli O157: H7) is one of the most common foodborne pathogens and is widespread in food and the environment. Thus, it is significant for rapidly detecting E. coli O157: H7. In this study, a colorimetric aptasensor based on aptamer-functionalized magnetic beads, exonuclease III (Exo III), and G-triplex/hemin was proposed for the detection of E. coli O157: H7. The functional hairpin HP was designed in the system, which includes two parts of a stem containing the G-triplex sequence and a tail complementary to cDNA. E. coli O157: H7 competed to bind the aptamer (Apt) in the Apt-cDNA complex to obtain cDNA. The cDNA then bound to the tail of HP to trigger Exo III digestion and release the single-stranded DNA containing the G-triplex sequence. G-triplex/hemin DNAzyme could catalyze TMB to produce visible color changes and detectable absorbance signals in the presence of H2O2. Based on the optimal conditions, E. coli O157: H7 could be detected down to 1.3 × 103 CFU/mL, with a wide linear range from 1.3 × 103 to 1.3 × 107 CFU/mL. This method had a distinguished ability to non-target bacteria, which showed good specificity. In addition, the system was successfully applied to detect E. coli O157: H7 in milk samples.

Dual-mode sensor based on GO-SELEX screening of aptamer for detecting cefapirin antibiotic residues in milk

The extensive use of cefapirin (CP) in milk has caused various health issues, resulting in an urgent need for an efficient assay for its detection. This study aimed to perform a colorimetric/fluorescence dual-mode assay based on graphene oxide–assisted systematic evolution of ligands by exponential enrichment (GO-SELEX) in vitro screening method for detecting CP aptamers. The aptamer (Apt22) had a high affinity (Kd = 13.818 ± 1.405 nM), with only 33 bases. Hence, we designed the G-quadruplex (G4) into a hairpin structure complemented by the shear effect of Exo III, and constructed a colorimetric/fluorescent dual-mode sensor. A colorimetric signal was generated using 3,3′,5,5′-tetramethylbenzidine discoloration catalyzed by a DNA-mimicking enzyme constructed from G4 and hemin. The formation of G4 implied that the hairpin structure was disrupted and the FAM and BHQ at the ends of it were separated, thus generating a fluorescent signal. Under optimal experimental conditions, the detection limits were 0.0168 and 0.0136 μM when the linear ranges of the colorimetric and fluorescent aptasensors were 1–8 μM and 0.9–2.3 μM. The sensor had high specificity and repeatability. It combined the advantages of visual colorimetric and fluorescence precision detection, providing a new approach to the practical monitoring of CP in milk.

A colorimetric aptasensor for CA125 determination based on dual catalytic performance of CeO2 nanozyme confined in macroporous silica foam.

A portable colorimetric aptasensor was constructed based on the dual catalytic performance of CeO2 nanozyme to determine carbohydrate antigen 125 (CA125). Firstly, CeO2 nanozyme was synthesized by calcination and ultrasonically dispersed in a macroporous silica foam (MSF) to form CeO2@MSF. Then the aptamer of CA125 (apt) and complementary DNA (c-DNA) were successively assembled on the CeO2@MSF to construct a CeO2@MSF/apt/c-DNA colorimetric aptasensor, which exhibited excellent oxidase-mimic performance and phosphatase-mimic activity simultaneously. In the presence of CA125, the apt specifically binds to target CA125, and the single-strand c-DNA leaves the CeO2@MSF/apt surface, which is catalytically hydrolyzed by exonuclease I. The produced phosphate ions inhibit the phosphatase-mimic activity of CeO2 nanozyme. Thus, the absorbance at 652nm of 3,3',5,5'-tetramethylbenzidine solution containing ascorbic acid-2-phosphate increases with the concentration of CA125. The response is linearly related to the logarithm of CA125 concentration from 1.0 to 10.0 U/mL under optimal experimental conditions. Based on this, the constructed colorimetric aptasensor has a high sensitivity, good selectivity, and high accuracy for CA125 determination in real human serum sample.

Colorimetric and photothermal dual-mode aptasensor with redox cycling amplification for the detection of ochratoxin A in corn samples

Ochratoxin A (OTA) detection is critical for public health safety. This study proposes a G-quadruplex-Hemin/iodide (G4-Hemin/I−)-mediated non-enzyme redox cycling amplification (RCA) system for dual-modal (colorimetric and photothermal thermometer) OTA analysis. The proposed aptasensor platform for point-of-care testing employs a common thermometer for quantitative signal readouts. The OTA aptamer folds into a G4 structure, which significantly enhances the catalytic activity in the presence of I− after RCA reaction. Moreover, a notable temperature enhancement causes color changes, providing an ultrasensitive and label-free platform for OTA detection. Further, the designed sensor was applied to OTA content determination in corn samples and achieved satisfactory results compared to a commercial enzyme-linked immunoassay kit. The proposed dual-mode aptasensor is simple, highly sensitive (1 pg/mL for colorimetric method, 0.8 pg/mL for photothermal method), selective, and suitable for low-cost instrument-free bioanalysis in low-resource settings.

Aptasensing biosynthesized phosphatidylserine with a AuNPs nanozyme-based colorimetric aptasensor

Sensitive monitoring of the target products during the biosynthesis process is crucial, and facile analytical approaches are urgently needed. Herein, phosphatidylserine (PS) was chosen as the model target, a colorimetric aptasensor was developed for the rapid quantitation in biosynthesis samples. A chimeric aptamer was constructed with two homogeneous original PS aptamers. Specific recognition between the chimeric aptamer and PS results in the desorption of aptamer from the surface of the AuNPs nanozyme, and the peroxidase-like enzymatic activity of the AuNPs nanozyme was weakened in a relationship with the different concentrations. The developed aptasensor performed well when applied for analyzing PS in biosynthesis samples. The aptasensor offers good sensitivity and selectivity, under optimal conditions, achieving monitoring and quantitation of PS in the range of 2.5–80.0 μmol/L, with a limit of detection at 536.2 nmol/L. Moreover, the aptasensor provides good accuracy, with comparison rates of 98.17 %–106.40 %, when compared with the HPLC-ELSD. This study provides a good reference for monitoring other biosynthesized products and promoting the development of aptamers and aptasensors in real-world applications.

Multi-signal aptasensor for thrombin detection based on catalytically active gold nanoparticles and fluorescent silicon quantum dots.

A multi-signal aptasensor for thrombin determination isproposed based on catalytically active gold nanoparticles (AuNPs) and fluorescent silicon quantum dots (SiQDs). Yellow 4-Nitrophenol (4-NP) could be converted to colorless 4-Aminophenol (4-AP) by catalytically active aptamer-modified AuNPs (S1-AuNPs). The SiQDs emitted strong blue fluorescence at 455nm at the excitation wavelength of 367nm. When thrombin was absent, S1-AuNPs could catalytically reduce yellow 4-NP to colorless 4-AP. When thrombin was added, the aptamer could be transformed into a G-quadruplex structure, which masked the surface-active catalytic sites of AuNPs and restrained the reduction of 4-NP. Thus, the fluorescence of SiQDs was greatly quenched by 4-NP through the inner filter effect (IFE), and the solution color remained yellow. As the concentration of thrombin increased, the catalytic activity of S1-AuNPs decreased. The concentration of 4-NP that was converted to 4-AP declined and the unconverted 4-NP increased. In this process, the absorption peak of 4-NP at 400nm increased while the fluorescence emission of SiQDs at 455nm decreased. The linear ranges of the fluorometric and colorimetric aptasensor were 0.5-30nM and 0.3-30nM, respectively. The limits of detection (LOD) for the two modes were 0.15nM and 0.13nM. Furthermore, a portable sensing platform was constructed by combining the smartphone-based device with the software ImageJ for the determination of thrombin. With the advantages of cost-effectiveness, simplicity of operation and broad applicability, this aptasensor provided a new perspective for on-site determinationof thrombin in the clinical field.

Precision-SELEX aptamer screening for the colorimetric and fluorescent dual-readout aptasensing of AFB1 in food

As nucleic acid-based affinity elements, aptamers have attracted significant attention for a wide range of analytical applications. Although several aflatoxin B1 (AFB1) aptamers have been identified, they are unsuitable for overcoming the unavoidable cross-reactions from interferents in complex food matrices due to their poor binding affinities and specificities. Herein, a novel precision-systematic evolution of ligands by exponential enrichment (P-SELEX) strategy through introducing the counter (matrix without target AFB1) and positive (with AFB1) screening steps was implemented to accurately identify AFB1 aptamers. A DNA aptamer A-42-2 at a 24-nt length was selected finally, which possessed nanomolar-level affinity of 5.55 nM, high specificity to other interferents, and strong anti-cross-reactivity ability for matrix components. Then, an A-42-2 aptamer-based ultra-sensitive colorimetric and fluorescent dual-readout aptasensor was fabricated for AFB1 detection in three kinds of complex food samples rich in starch without cross-reactions. The aptasensor displayed outstanding detection capacity with a wide liner range of 0.25–30 nM (1.95–234.4 μg/kg), while the detection limit for colorimetric measurement as low as 0.22 nM (1.72 μg/kg) and 0.048 nM (0.20 μg/kg) for fluorescent determination. P-SELEX is ideal for screening and applying aptamers in complex food matrices, creating more opportunities for the efficient and cost-effective development of high-quality aptamers and aptasensors for other targets.

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 5-300ng/mL. A linear regression equation is Y=0.0003X+0.5128 (R2=0.9989) and a limit of detection is 5ng/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 15min to complete. The smartphone assisted colorimetric aptamer sensor can be used for the detection of zearalenone in maize.

A novel colorimetric and fluorescent dual-mode 3D paper-based microfluidic aptasensor for the point-of-care detection of sulfadimethoxine

Sulfadimethoxine antibiotics (SDM) are commonly used in aquatic foods to inhibit bacteria, but their residues in aquatic food pose certain risks to public health. Herein, we developed a systematic portable biosensing platform for SDM, which comprised a dual-mode three-dimensional paper-based microfluidic chip (3D-μPAD), a dual-light portable device, and a smartphone application for obtaining results. The detection principle of the dual-mode 3D-μPAD was based on the aggregation of Ag NPs without the protection of aptamers and the inner filter effect (IFE) between Mg, N-CDs and Ag NPs. With the addition of SDM, the significant change of two signals can be sensitively recognized in the portable device and calculated by a self-developed mini program in the smartphone to obtain the detection results. Under optimal conditions, SDM was sensitively detected in the range of 10–1000 ng/mL with an estimated limit of detection (LOD) of 0.13 ng/mL and 0.21 ng/mL in fluorescence and colorimetric modes, respectively. Moreover, this platform was successfully applied to determine SDM in fish with recoveries of 96.7%− 113.6% and 98.2%− 105.1%, respectively. This method has the advantages of low detection cost, low reagent consumption, and unlimited instruments and operators, which better fulfills the point-of-care needs of hazards analysis in food.

MnO2 nanoflowers based colorimetric and fluorescent dual-mode aptasensor for sensitive detection of aflatoxin B1 in milk

Aflatoxin B1 (AFB1) with tremendous toxic effects has caused a serious threat to food security. Accurate quantification of AFB1 in food can effectively prevent the risk of human intake of AFB1. Herein, a colorimetric and fluorescent dual-mode aptasensor for accurate and sensitive detection of AFB1 has been developed based on MnO2 nanoflowers (MnO2NFs) for the first time. MnO2NFs could catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) into blue oxidation product (TMBox) by H2O2, which would be used for visible detection of AFB1. Simultaneously, MnO2NFs can be served as a signal amplifier and reduced by ascorbic acid to generate lots of Mn2+ which would quench the fluorescence of calcein for fluorescent detection of AFB1. Both colorimetric and fluorescent methods have been successfully applied for determination of AFB1 in milk samples with satisfactory results. The proposed dual-mode detection method with high detection sensitivity and accuracy showed great promise for monitoring AFB1 in food.

Aptamers selected and identified as a colorimetric dual-mode sensing platform for selective and sensitive detection of capsaicin

Capsaicin (CAP), a prominent indicator, has been identified for detecting the gutter oil in adulterated edible oils. In view of the limited availability of efficient and reliable methods for detecting gutter oil, the present study employed the Capture-SELEX technology, which utilizes a high-throughput sequencing (HTS) platform, to facilitate the precise tracking of screening rounds and facilitate the isolation of aptamers with specific affinity for CAP. Isothermal titration calorimetry (ITC) determined the highest affinity and Kd value of 15.5 ± 4.69 nM for aptamer Cap-1. A colorimetric dual-mode aptasensor was designed for CAP detection based on graphene oxide (GO)@gold nanoparticles (AuNPs) composite. A high-sensitivity assay can be achieved using a Synergy™ H1 multimode zymography instrument and a smartphone. Under optimal conditions, the colorimetric dual-mode aptasensor has a detection range of 0.5 ∼ 120 ng mL−1 and a low limit of detection (LOD) of 0.14 ng mL−1. The quantitative recovery of the sensor for CAP in edible oil was 86.25∼98.12 %. Compared with the conventional single-mode aptasensor, the dual-mode aptasensor has independent signal conversion, which provides suitable detection solutions for different scenarios and improves detection accuracy and reliability.

A label-free aptasensor for colorimetric detection of food toxin: Mediation of catalytically active gold nanozymes and smartphone imaging strategy

A portable colorimetric aptasensor was developed on the surface of a plastic sheet for on-site detection of acrylamide. The mechanism of aptasensor is based on the disruption of the aptamer complex with its complementary strand on the sensing zone, and subsequently, the catalytic activity of gold nanoparticles (AuNPs) for the reduction process of 4-nitrophenol (4-NP) in the presence of sodium borohydride (NaBH4). A yellow-to-colorless change of the sample solution revealed the target presence, easily discernible by the naked eye. The acrylamide quantification was accomplished using the smartphone imaging readout technique. The aptasensor detected the acrylamide concentration in the range of 0.01–500 nmol L−1 with a detection limit of 0.0024 nmol L−1. Coffee, potato chips, bread, and lake water samples were successfully analyzed by the aptasensor for their acrylamide content. The introduced aptasensor can pave a facile, cost-effective, portable, and user-friendly sensing tool for food safety control and environmental monitoring.

Label-free colorimetric sensor for Pb2+ determination using catalytic activity of MnO2 nanoflowers and elongated aptamer

In this study, a label-free aptasensor utilizing colorimetric properties was developed to detect Pb2+ with high sensitivity. The approach involved applying modified aptamer which enhanced the oxidase-mimicking activity of MnO2 nanoflowers. This innovative method provides an efficient means for monitoring Pb2+ ions without requiring any labeling techniques. The fundamental principle of this aptasensor is based on the adsorption of a modified aptamer onto MnO2 nanoflowers' surface, which in turn increases their affinity for chromogenic substrates and enhances their catalytic activity. The proposed aptasensor exploits the high sensitivity due to the extension of the aptamer sequence length by terminal deoxynucleotidyl transferase (TdT). Under optimum experimental conditions, the developed colorimetric aptasensor indicated a linear detection range from 4 to 80 nM with a limit of detection (LOD) of 1.4 nM. Moreover, the aptasensor successfully monitored Pb2+ in the drinking water, milk and human serum samples. Henceforth, the colorimetric aptasensor exhibited in this study possesses several benefits such as uncomplicated operation, cost-effectiveness, label-free detection and remarkable sensitivity. Thus rendering it a suitable option for analyzing intricate samples.

A colorimetric aptasensor for detecting ochratoxin A based on label-free aptamer and gold nanozyme.

In this study, the aptamer of ochratoxin A (OTA) increased the negative charge density on the surface of gold nanoparticles (AuNPs) and promoted the release of hydroxyl radicals and Au3+ to enhance the peroxidase-like activity of the AuNPs. The OTA bound only to the aptamer and did not adsorb non-specifically to the AuNPs. Based on these two conclusions, a label-free colorimetric aptasensor was successfully developed, enabling the precise detection of OTA within the concentration range of 10-600nM, with a remarkably low detection limit of 6.20nM. The colorimetric aptasensor was applied to detect OTA in oats, corn, soybeans, rice, and glutinous rice.

A robust and facile colorimetric aptasensor for the detection of Salmonella Typhimurium based on the regulation of Fe3O4@Cu@PCPy yolk-shell nanozyme activity

Due to their superparamagnetism and enzyme-like activity, iron oxide (Fe3O4) nanozymes can be readily used for sample pretreatment and the generation of detection signals, and have, thus, attracted much attention in the field of bioanalysis and diagnosis. However, the low catalytic activity of Fe3O4 nanozymes does reduce the sensitivity of Fe3O4-based methods, limiting their application. In this study, Fe3O4@Cu@poly(pyrrole-2-carboxylic acid) yolk-shell nanozymes (Fe3O4@Cu@PCPy YSNs) were synthesized using a facile approach and selective chemical etching technology. Compared with Fe3O4 nanozymes, the Fe3O4@Cu@PCPy YSNs demonstrated a three-fold increase in the peroxidase-like activity, good dispersity and strong superparamagnetism. In addition, the flower-shaped structure of aptamer-complementary strand (Apt-CS) conjugates was designed on the surface of the Fe3O4@Cu@PCPy YSNs, which effectively inhibited their peroxidase-like activity by creating a physical barrier that hindered the access of substrates to the center of the Fe3O4@Cu@PCPy YSNs. Based on this principle, a robust and facile colorimetric aptasensor was developed for detecting Salmonella Typhimurium. The flower-shaped Apt-CS were dissociated in the presence of S. Typhimurium, promoting the recovery of Fe3O4@Cu@PCPy YSN catalytic activity. Under optimized conditions, this proposed aptasensor successfully detected S. Typhimurium in a linear range of 3 to 3 × 106 CFU/mL, achieving a detection limit of 1 CFU/mL. Finally, the feasibility of this novel aptasensor was further validated by three actual samples, with recoveries of between 84.3% and 102%, thereby demonstrating the huge potential of the proposed aptasensor for detecting S. Typhimurium in foods.

An ultrasensitive aptasensor for exosomes detection based on biotin-streptavidin and MXenes

Exosomes derived from lung cancer typically contain the genetic information of the donor cells. Therefore, exosomes contribute to early diagnosis, treatment effectiveness evaluation, and prognosis assessment of cancer. Based on the biotin-streptavidin system and MXenes nanomaterial, a dual-effect amplification method had been developed to construct an ultrasensitive colorimetric aptasensor for detecting exosomes. MXenes can enhance the loading of aptamer and biotin as the high specific surface area. Biotin-streptavidin system can increase the amount of horseradish peroxidase-linked (HRP-linked) streptavidin, considerably boosting the color signal of the aptasensor. The proposed colorimetric aptasensor exhibited excellent sensitivity, with a detection limit of 42 particles μL−1 and a linear range of 102 to 107 particles μL−1. The constructed aptasensor showed satisfactory reproducibility, stability, and selectivity, confirming the promising application of exosomes in clinical cancer detection.