Dipstick-type biosensor for visual detection of DNA with oligonucleotide-decorated colored polystyrene microspheres as reporters

"Blue-red-purple" multicolored lateral flow immunoassay for simultaneous detection of GM crops utilizing RPA and CRISPR/Cas12a

Advanced multiplexed testing techniques should be designed and developed to ensure an accurate and reliable evaluation for unknown samples. In this study, an efficient platform coupled with the "Blue-Red-Purple" strategy based on recombinant polymerase amplification (RPA), CRISPR/Cas12a and lateral flow strip was established, which could realize the dual-target detection of CP4-EPSPS and Cry1Ab/Ac in genetically modified crops. The lateral flow immunoassay was developed using different colored microspheres to label the antibodies to realize the visualization of results and avoid cross-reactions. The proposed method exhibits high specificity, sensitivity and stability. The visual detection limits of standard plasmids and real samples reached 10 copies/μL and 0.5 %, respectively, which could be stored at 4 °C for 12 months with high detection ability. Moreover, the entire detection process could be completed within 50 min without any complex instruments or professional operators. These findings indicated that a sensitive, specific, rapid and accurate method was established for on-site detection of GM crops.

Design and Evaluation of Multiplex One-Step Reverse Transcription PCR-Dipstick Chromatography Method for the Analysis of Seven Respiratory Pathogens

Influenza A, influenza B, severe acute respiratory syndrome coronavirus 2, adenovirus, respiratory syncytial virus, Mycoplasma pneumoniae, and Chlamydophila pneumoniae are common pathogens that can cause severe pneumonia and other symptoms, resulting in acute lower respiratory tract infections. The objective of this study was to design and evaluate a sensitive and specific multiplex one-step reverse transcription PCR (RT-PCR)–dipstick chromatography method for simultaneous rapid detection of these seven pathogens. Streptavidin-coated blue latex particles were used to read out a positive signal. Based on the DNA–DNA hybridization of oligonucleotide sequences (Tag) for forward primer with the complementary oligonucleotide sequence (cTag) on the dipstick and biotin–streptavidin interactions, PCR products were able to be illuminated visually on the dipstick. The specificity and the limit of detection (LOD) were also evaluated. Moreover, the clinical performance of this method was compared with Sanger sequencing for 896 samples. No cross reaction with other pathogens was found, confirming the high specificity of this method. The LOD was 10 copies/µL for each of the tested pathogens, and the whole procedure took less than 40 min. Using 896 samples, the sensitivity and specificity were shown to be no lower than 94.5%. The positive predictive value was higher than 82.1%, and the negative predictive value was higher than 99.5%. The kappa value between the PCR–dipstick chromatography method and Sanger sequencing ranged from 0.869 to 0.940. In summary, our one-step RT-PCR–dipstick chromatography method is a sensitive and specific tool for rapidly detecting multiplex respiratory pathogens.

Nucleic Acid-Based Lateral Flow Biosensor for Salmonella Typhi and Salmonella Paratyphi: A Detection in Stool Samples of Suspected Carriers

A multiplex rapid detection system, based on a PCR-lateral flow biosensor (mPCR-LFB) was developed to identify Salmonella Typhi and Salmonella Paratyphi A from suspected carriers. The lower detection limit for S. Typhi and S. Paratyphi A was 0.16 and 0.08 ng DNA equivalent to 10 and 10² CFU/mL, respectively. Lateral flow biosensor was used for visual detection of mPCR amplicons (stgA, SPAint, ompC, internal amplification control) by labeling forward primers with fluorescein-isothiocyanate (FITC), Texas Red, dinitrophenol (DNP) and digoxigenin (DIG) and reverse primers with biotin. Binding of streptavidin-colloidal gold conjugate with the amplicons resulted in formation of a red color dots on the strip after 15-20 min of sample exposure. The nucleic acid lateral flow analysis of the mPCR-LFB was better in sensitivity and more rapid than the conventional agarose gel electrophoresis. Moreover, the mPCR-LFB showed 100% sensitivity and specificity when evaluated with stools spiked with 100 isolates of Salmonella genus and other bacteria. A prospective cohort study on stool samples of 1176 food handlers in outbreak areas (suspected carriers) resulted in 23 (2%) positive for S. Typhi. The developed assay has potential to be used for rapid detection of typhoid carriers in surveillance program.

Visual detection of in vitro nucleic acid replication by submicro- and nano-sized materials

The rapid growth of in vitro nucleic acid replication has offered a powerful tool for clinical diagnosis, food safety detection and environmental monitorning. Successful implementation of various isothermal nucleic acid amplification methods enables rapid replication of target sequences without the participant of a thermal cycler. Point-of-need analysis possesses great superiorities in user-friendly, instant results analysis, low manufacturing, and consumable costs. To meet the great challenge of point-of-need analysis, developing simple and rapid visual methods becomes crucial. Submicro- and nanomaterials possess unique surface properties, which enables their rapid response to DNA amplicons. Their unique optical, magnetic, catalytic, and other physical/chemical properties have been frequently employed for the visual detection of in vitro nucleic acid replications. Herein, we aim to review the submicro- and nanomaterials-based visual methods for detection of nucleic acid amplification. The visual methods are classified according to the designing strategies (e.g. LSPR, bridging flocculation, luminescence, catalytic reaction, separation, etc.). The basic principles, merits and drawbacks of each strategy are described. The application in analysis of nucleic acid targets and non-nucleic acid targets are discussed. The main challenges and future research directions are also highlighted in this rapidly emerging field.

Multiplex loop-mediated isothermal amplification-based lateral flow dipstick for simultaneous detection of 3 food-borne pathogens in powdered infant formula

In this study, we established a rapid, simple, and sensitive method for visual and point-of-care detection of Salmonella spp., Cronobacter spp., and Staphylococcus aureus in powdered infant formula (PIF) based on multiplex loop-mediated isothermal amplification (mLAMP) combined with lateral flow dipstick (LFD). Three different species-specific target genes, siiA of Salmonella spp., internal transcribed space (ITS) of Cronobacter spp., and nuc of Staph. aureus, were applied in the mLAMP with biotin-, digoxin-, and Texas Red-modified forward inner primers and fluorescein isothiocyanate (FITC)-modified backward inner primers. After mLAMP, a large number of modified amplicons were detected with LFD; one end of the amplicon was conjugated to the anti-FITC antibody on gold nanoparticles and the other end to streptavidin (anti-digoxin or anti-Texas Red antibody) on test lines. Visual inspection of the device relies on the presence of a red band formed by accumulation of sandwich composites. The detection limits of this mLAMP-LFD assay for Salmonella spp., Cronobacter spp., and Staph. aureus in PIF without enrichment were 4.2, 2.6, and 3.4 cfu/g, respectively. The whole method can be completed in less than 1 h. Thus, mLAMP-LFD is a rapid and efficient method for simultaneously detecting Salmonella spp., Cronobacter spp., and Staph. aureus in PIF.

The Evolution of Polystyrene as a Cell Culture Material

Polystyrene (PS) has brought in vitro cell culture from its humble beginnings to the modern era, propelling dozens of research fields along the way. This review discusses the development of the material, fabrication, and treatment approaches to create the culture material. However, native PS surfaces poorly facilitate cell adhesion and growth in vitro. To overcome this, liquid surface deposition, energetic plasma activation, and emerging functionalization methods transform the surface chemistry. This review seeks to highlight the many potential applications of the first widely accepted polymer growth surface. Although the majority of in vitro research occurs on two-dimensional surfaces, the importance of three-dimensional (3D) culture models cannot be overlooked. The methods to transition PS to specialized 3D culture surfaces are also reviewed. Specifically, casting, electrospinning, 3D printing, and microcarrier approaches to shift PS to a 3D culture surface are highlighted. The breadth of applications of the material makes it impossible to highlight every use, but the aim remains to demonstrate the versatility and potential as both a general and custom cell culture surface. The review concludes with emerging scaffolding approaches and, based on the findings, presents our insights on the future steps for PS as a tissue culture platform.

Quantitative analysis of cell-free DNA in ovarian cancer

The aim of the present study was to investigate the association between cell-free DNA (cf-DNA) levels and clinicopathological characteristics of patients with ovarian cancer using a branched DNA (bDNA) technique, and to determine the value of quantitative cf-DNA detection in assisting with the diagnosis of ovarian cancer. Serum specimens were collected from 36 patients with ovarian cancer on days 1, 3 and 7 following surgery, and additional serum samples were also collected from 22 benign ovarian tumor cases, and 19 healthy, non-cancerous ovaries. bDNA techniques were used to detect serum cf-DNA concentrations. All data were analyzed using SPSS version 18.0. The cf-DNA levels were significantly increased in the ovarian cancer group compared with those of the benign ovarian tumor group and healthy ovarian group (P<0.01). Furthermore, cf-DNA levels were significantly increased in stage III and IV ovarian cancer compared with those of stages I and II (P<0.01). In addition, cf-DNA levels were significantly increased on the first day post-surgery (P<0.01), and subsequently demonstrated a gradual decrease. In the ovarian cancer group, the area under the receiver operating characteristic curve of cf-DNA and the sensitivity were 0.917 and 88.9%, respectively, which was higher than those of cancer antigen 125 (0.724, 75%) and human epididymis protein 4 (0.743, 80.6%). There was a correlation between the levels of serum cf-DNA and the occurrence and development of ovarian cancer in the patients evaluated. bDNA techniques possessed higher sensitivity and specificity than other methods for the detection of serum cf-DNA in patients exhibiting ovarian cancer, and bDNA techniques are more useful for detecting cf-DNA than other factors. Thus, the present study demonstrated the potential value for the use of bDNA as an adjuvant diagnostic method for ovarian cancer.

Development of a dry-reagent-based nucleic acid-sensing platform by coupling thermostabilised LATE-PCR assay to an oligonucleotide-modified lateral flow biosensor

In this study, we report for the first time the development of a dry-reagent-based nucleic acid-sensing platform by combining a thermostabilised linear-after-the-exponential (LATE)-PCR assay with a one-step, hybridisation-based nucleic acid lateral flow biosensor. The nucleic acid-sensing platform was designed to overcome the need for stringent temperature control during transportation or storage of reagents and reduces the dependency on skilled personnel by decreasing the overall assay complexity and hands-on time. The platform was developed using toxigenic Vibrio cholerae as the model organism due to the bacterium's propensity to cause epidemic and pandemic cholera. The biosensor generates result which can be visualised with the naked eyes and the limit of detection was found to be 1pg of pure genomic DNA and 10CFU/ml of toxigenic V. cholerae. The dry-reagent-based nucleic acid-sensing platform was challenged with 95 toxigenic V. cholerae, 7 non-toxigenic V. cholerae and 66 other bacterial strains in spiked stool sample and complete agreement was observed when the results were compared to that of monosialoganglioside (GM1)-ELISA. Heat-stability of the thermostabilised LATE-PCR reaction mixes at different storage temperatures (4-56°C) was investigated for up to 90days. The dry-reagent-based genosensing platform with ready-to-use assay components provides an alternative method for sequence-specific detection of nucleic acid without any cold chain restriction that is associated with conventional molecular amplification techniques.

Promising Nucleic Acid Lateral Flow Assay Plus PCR for Shiga Toxin-Producing Escherichia coli

Shiga toxin (Stx)-producing Escherichia coli (STEC) is a frequent cause of foodborne infections, and methods for rapid and reliable detection of STEC are needed. A nucleic acid lateral flow assay (NALFA) plus PCR was evaluated for detecting STEC after enrichment. When cell suspensions of 45 STEC strains, 14 non-STEC strains, and 13 non-E. coli strains were tested with the NALFA plus PCR, all of the STEC strains yielded positive results, and all of the non-STEC and non-E. coli strains yielded negative results. The lower detection limit for the STEC strains ranged from 0.1 to 1 pg of genomic DNA (about 20 to 200 CFU) per test, and the NALFA plus PCR was able to detect Stx1- and Stx2-producing E. coli strains with similar sensitivities. The ability of the NALFA plus PCR to detect STEC in enrichment cultures of radish sprouts, tomato, raw ground beef, and beef liver inoculated with 10-fold serially diluted STEC cultures was comparable to that of a real-time PCR assay (at a level of 100 to 100,000 CFU/ml in enrichment culture). The bacterial inoculation test in raw ground beef revealed that the lower detection limit of the NALFA plus PCR was also comparable to that obtained with a real-time PCR assay that followed the U.S. Department of Agriculture guidelines. Although further evaluation is required, these results suggest that the NALFA plus PCR is a specific and sensitive method for detecting STEC in a food manufacturing plant.

Lateral flow devices for nucleic acid analysis exploiting quantum dots as reporters

There is a growing interest in the development of biosensors in the form of simple lateral flow devices that enable visual detection of nucleic acid sequences while eliminating several steps required for pipetting, incubation and washing out the excess of reactants. In this work, we present the first dipstick-type nucleic acid biosensors based on quantum dots (QDs) as reporters. The biosensors enable sequence confirmation of the target DNA by hybridization and simple visual detection of the emitted fluorescence under a UV lamp. The 'diagnostic' membrane of the biosensor contains a test zone (TZ) and a control zone (CZ). The CZ always fluoresces in order to confirm the proper function of the biosensor. Fluorescence is emitted from the TZ, only when the specific nucleic acid sequence is present. We have developed two general types of QD-based nucleic acid biosensors, namely, Type I and Type II, in which the TZ consists of either immobilized streptavidin (Type I) or immobilized oligodeoxynucleotides (Type II). The control zone consists of immobilized biotinylated albumin. No purification steps are required prior to the application of the DNA sample on the strip. The QD-based nucleic acid biosensors performed accurately and reproducibly when applied to (a) the visual detection of PCR amplification products and (b) visual genotyping of single nucleotide polymorphisms (SNPs) in human genomic DNA from clinical samples. As low as 1.5 fmol of double-stranded DNA were clearly detected by naked eye and the dynamic range extended to 200 fmol. The %CV were estimated to be 4.3-8.2.

Rapid and sensitive PCR-dipstick DNA chromatography for multiplex analysis of the oral microbiota

A complex of species has been associated with dental caries under the ecological hypothesis. This study aimed to develop a rapid, sensitive PCR-dipstick DNA chromatography assay that could be read by eye for multiplex and semiquantitative analysis of plaque bacteria. Parallel oligonucleotides were immobilized on a dipstick strip for multiplex analysis of target DNA sequences of the caries-associated bacteria, Streptococcus mutans, Streptococcus sobrinus, Scardovia wiggsiae, Actinomyces species, and Veillonella parvula. Streptavidin-coated blue-colored latex microspheres were to generate signal. Target DNA amplicons with an oligonucleotide-tagged terminus and a biotinylated terminus were coupled with latex beads through a streptavidin-biotin interaction and then hybridized with complementary oligonucleotides on the strip. The accumulation of captured latex beads on the test and control lines produced blue bands, enabling visual detection with the naked eye. The PCR-dipstick DNA chromatography detected quantities as low as 100 pg of DNA amplicons and demonstrated 10- to 1000-fold higher sensitivity than PCR-agarose gel electrophoresis, depending on the target bacterial species. Semiquantification of bacteria was performed by obtaining a series of chromatograms using serial 10-fold dilution of PCR-amplified DNA extracted from dental plaque samples. The assay time was less than 3 h. The semiquantification procedure revealed the relative amounts of each test species in dental plaque samples, indicating that this disposable device has great potential in analysis of microbial composition in the oral cavity and intestinal tract, as well as in point-of-care diagnosis of microbiota-associated diseases.

An internal amplification control for quantitative nucleic acid analysis using nanoparticle-based dipstick biosensors

Quantitative analysis of virus nucleic acids is essential for monitoring the efficacy of medical treatment based on the copy numbers of virus's RNA or DNA in blood. To quantitatively detect virus nucleic acids in blood, here an internal amplification control (IAC) coupled with a nanoparticle-based DNA biosensor was proposed. The IACs with a specific sequence were designed and spiked into serum before nucleic acids extraction. Sequences of the IACs and the targets only differ in the base order of one PCR priming site; thus, the IACs and the targets are identical in Tm, giving the same amplification efficiency during PCR. To visually detect amplicons, a dipstick biosensor based on streptavidin-functionalized nanoparticles is employed. By comparing color densities of a test zone with an IAC zone on the biosensor, the content of the target in serum can be semi-quantitatively analyzed. This approach has achieved the detection of HBV DNA at approximately 100 copies of the pathogen load. The feasibility of this method is demonstrated by successful semi-quantification of pathogen load in 30 clinical samples from HBV-infected patients. These data indicate that the introduction of an IAC and nanoparticle-based dipstick-type biosensor could be a powerful tool in point of care testing (POCT).

Ambient temperature detection of PCR amplicons with a novel sequence-specific nucleic acid lateral flow biosensor

In the field of diagnostics, molecular amplification targeting unique genetic signature sequences has been widely used for rapid identification of infectious agents, which significantly aids physicians in determining the choice of treatment as well as providing important epidemiological data for surveillance and disease control assessment. We report the development of a rapid nucleic acid lateral flow biosensor (NALFB) in a dry-reagent strip format for the sequence-specific detection of single-stranded polymerase chain reaction (PCR) amplicons at ambient temperature (22-25°C). The NALFB was developed in combination with a linear-after-the-exponential PCR assay and the applicability of this biosensor was demonstrated through detection of the cholera toxin gene from diarrheal-causing toxigenic Vibrio cholerae. Amplification using the advanced asymmetric PCR boosts the production of fluorescein-labeled single-stranded amplicons, allowing capture probes immobilized on the NALFB to hybridize specifically with complementary targets in situ on the strip. Subsequent visual formation of red lines is achieved through the binding of conjugated gold nanoparticles to the fluorescein label of the captured amplicons. The visual detection limit observed with synthetic target DNA was 0.3 ng and 1 pg with pure genomic DNA. Evaluation of the NALFB with 164 strains of V. cholerae and non-V. cholerae bacteria recorded 100% for both sensitivity and specificity. The whole procedure of the low-cost NALFB, which is performed at ambient temperature, eliminates the need for preheated buffers or additional equipment, greatly simplifying the protocol for sequence-specific PCR amplicon analysis.

Dipstick test for DNA-based food authentication. Application to coffee authenticity assessment

This paper reports DNA-based food authenticity assays, in which species identification is accomplished by the naked eye without the need of specialized instruments. Strongly colored nanoparticles (gold nanoparticles) are employed as reporters that enable visual detection. Furthermore, detection is performed in a low-cost, disposable, dipstick-type device that incorporates the required reagents in dry form, thereby avoiding multiple pipetting and incubation steps. Due to its simplicity, the method does not require highly qualified personnel. The procedure comprises the following steps: (i) PCR amplification of the DNA segment that flanks the unique SNP (species marker); (ii) a 15 min extension reaction in which DNA polymerase extends an allele-specific primer only if it is perfectly complementary with the target sequence; (iii) detection of the products of the extension reaction within a few minutes by the naked eye employing the dipstick. No purification is required prior to application of the extension products to the dipstick. The method is general and requires only a unique DNA sequence for species discrimination. The only instrument needed is a conventional thermocycler for PCR, which is common equipment in every DNA laboratory. As a model, the method was applied to the discrimination of Coffea robusta and arabica species in coffee authenticity assessment. As low as 5% of Robusta coffee can be detected in the presence of Arabica coffee.

Nucleic acid lateral flow tests for molecular diagnosis: an update

Lateral flow tests for molecular diagnosis have enormous potential in the fields of clinical practice, food safety, genotyping and environmental contamination. This paper describes the basic features of nucleic acid lateral flow (NALF) tests and some recent evolutions in this domain. The paper intentionally does not report on the accuracy of NALF tests, a largely under-investigated aspect of these tests. As for lateral flow immunoassays, NALF tests are intended to simplify detection of an analyte. Thus, designing NALF tests that are less dependent on or independent of sophisticated equipment remains a major challenge.

Fluorescent strip sensor for rapid determination of toxins

Here, we report a simple fluorescent strip sensor based on aptamer-quantum dots technology that can meet toxin monitoring demands using ochratoxin A (OTA) as a model toxin. The limit of the detection (LOD) for the fluorescent strip was 1.9 ng mL(-1), while the time needed for the detection is only 10 min; this conforms to the standards of World Health Organization (WHO) or better. Overall functional parameters are also better than the analogous characteristics of gold nanoparticle strips. High selectivity was maintained as well, making them suitable for the samples with complex solution composition.

Multianalyte, dipstick-type, nanoparticle-based DNA biosensor for visual genotyping of single-nucleotide polymorphisms

DNA biosensors involve molecular recognition of the target sequence by hybridization with specific probes and detection by electrochemical, optical or gravimetric transduction. Disposable, dipstick-type biosensors have been developed recently, which enable visual detection of DNA without using instruments. In this context, we report a multianalyte DNA biosensor for visual genotyping of two single-nucleotide polymorphisms (SNPs). As a model, the biosensor was applied to the simultaneous genotyping of two SNPs, entailing the detection of four alleles. A PCR product that flanks both polymorphic sites is subjected to a single primer extension (PEXT) reaction employing four allele-specific primers, each containing a region complementary to an allele and a characteristic segment that enables subsequent capture on a test zone of the biosensor. The primers are extended with dNTPs and biotin-dUTP only if there is perfect complementarity with the interrogated sequence. The PEXT mixture is applied to the biosensor. As the developing buffer migrates along the strip, all the allele-specific primers are captured by immobilized oligonucleotides at the four test zones of the biosensor and detected by antibiotin-functionalized gold nanoparticles. As a result, the test zones are colored red if extension has occurred denoting the presence of the corresponding allele in the original sample. The excess nanoparticles are captured by immobilized biotinylated albumin at the control zone of the sensor forming another red zone that indicates the proper performance of the system. The assay was applied successfully to the genotyping of twenty clinical samples for two common SNPs of MBL2 gene.