Phenol red as electrochemical indicator for highly sensitive quantification of SARS-CoV-2 by loop-mediated isothermal amplification detection

Facilitating self-testing with a fast, accurate, and simplified shelf-stable colorimetric LAMP system for Mpox and SARS-CoV-2 detection

The rapid and accurate detection of viral infections is essential for effective disease management and prevention. Quantitative polymerase chain reaction (qPCR) remains the gold standard for viral detection due to its high sensitivity and specificity. However, its limitations-including the need for specialized equipment, trained personnel, and longer processing times-make it impractical for at-home or rapid testing. Although numerous point-of-care assays based on isothermal nucleic acid amplification have been developed, they often lack the simplicity and adaptability required for self-testing in non-laboratory settings such as at home. To address this, we developed and validated the SCOLAR (Shelf-stable Colorimetric LAMP system for Rapid self-testing of viruses) system, a simplified, portable, and accurate diagnostic tool designed for self-testing of Mpox and SARS-CoV-2 infections. The SCOLAR system employs novel lyophilized colorimetric loop-mediated isothermal amplification (LAMP) beads, a customized sample lysis buffer, and smartphone-assisted RGB color analysis for interpreting results. Validation was conducted using 24 mock Mpox skin swabs, 32 wastewater samples, and 104 clinical SARS-CoV-2 nasopharyngeal swabs, with comparisons to an in-house qPCR assay. The SCOLAR system demonstrated an analytical sensitivity of below 10 copies/μL for all targets within 15 min. Diagnostic performance for mock Mpox samples exhibited 93.8 % sensitivity and 100 % specificity, while wastewater samples achieved 100 % sensitivity and specificity. SARS-CoV-2 swabs had 96 % sensitivity and 100 % specificity. The system also proved effective for self-testing by untrained individuals. SCOLAR offers a reliable, easy-to-use platform for rapid self-testing, with potential for broader applications in public health strategies to enhance pandemic preparedness and response.

ElectrochemCap: an integrated detection for loop-mediated isothermal amplification reactions

Loop-mediated isothermal amplification (LAMP) of genetic materials has emerged as a powerful molecular biology technique with great potential to be a standard point-of-care (POC) technique. This method has found several applications, but it still presents challenges for its direct on-site application, particularly in terms of integrated reaction and detection systems and the risk of carryover contamination. In this work, we propose an innovative solution - an electrochemical microcentrifuge tube cap (ElectrochemCap) based on a screen-printed electrode, a 3D printed adapter and an adhesive layer - which integrates the amplification reaction and its subsequent electrochemical detection in a single device. The design, fabrication, and electrochemical characterization of the ElectrochemCap are reported here, demonstrating its suitability for LAMP detection. Rapidly emerging technologies, such as 3D printing or xurography, are the basis of a prototype that has been validated for the detection of SARS-CoV-2 using reverse transcription LAMP (RT-LAMP), achieving results comparable to those obtained by gold-standard RT-qPCR. Moreover, we have explored the versatility of the ElectrochemCap presenting several additional designs (for containers with different volumes, shapes and materials, as well as multiplexed approaches), expanding its potential applications. Overall, the ElectrochemCap represents an affordable, versatile, and marketable innovation for integrated quantitative electrochemical detection, with enormous possibilities in bioelectroanalytical procedures and portable laboratory setups.

Short-stranded DNA segment-modulated LAMP/H+ as signal transducer to guide CHA-cooperated amplifiable electrochemical biosensing

BACKGROUND

Modulating loop-mediated isothermal amplification (mLAMP) by short-stranded DNA segment trigger (T) to generate byproducts H+ ions (mLAMP/H+) as signal transducer is intriguing for developing catalytic hairpin assembly (CHA)-cooperated amplifiable electrochemical biosensors. This would be a big challenge for traditional LAMP that is basically suitable for amplifying long-stranded oligonucleotides up to 200-300 nt. To address this inherent limitation of traditional LAMP, many researchers have put in efforts to explore improvements in this that would allow LAMP to be used for a wider range of target species amplification.

RESULTS

Here in this work, we are inspired to explore two-step loop-mediated amplification, firstly forming T-activated double-loop dumbbell structure (DLDS) intermediate by a recognition hairpin and a hairpin precursor, and next DLDS-guided mLAMP process with the aid of two primers to yield mLAMP/H+ during successive DNA incorporation via nucleophilic attacking interaction. To manipulate the mLAMP/H+-directed transduction of input T, a pH-responsive triplex strand is designed with the ability of self-folding in Hoogsteen structure at slightly acidic conditions, resulting in the dehybridization of a fuel strand (FS) to participate in CHA between two hairpins on the modified electrode surface, in which FS is repetitively displaced and recycled to fuel the progressive CHA events. In the as-assembled dsDNA complexes, numerous electroactive ferrocene labels are immobilized in the electrode sensing interface, thereby generating significantly amplified electrochemical current signal that can sense the presented and varied T.

SIGNIFICANCE

It is clear that we have creatively constructed a unique electrochemical biosensor for disease detection. Benefited from the rational combination of mLAMP and CHA, our electrochemical strategy is highly sensitive, specific and simplified, and would provide a new paradigm to construct various mLAMP/H+-based biosensors for other short-stranded DNA or microRNAs markers.

Photochromic visual sensing chip for isothermal amplification detection of porcine transmissible gastroenteritis virus

The outbreak of transmissible gastroenteritis virus (TGEV) will cause huge economic losses to the whole pig industry. Hence, there is urgent need to develop a rapid and ultrasensitive method for detection of TGEV. As a nucleic acid detection technique, loop-mediated isothermal amplification (LAMP) can achieve quantitative detection of targeted nucleic acids with high sensitivity and selectivity. Nevertheless, the signal outputs of LAMP method must be acquired by complicated instruments. In this work, we firstly developed a LAMP photochromic sensing chip for porcine TGEV detection by combination of the photochromic sensing chip and nucleic acid amplification. The detection signal was based on color change of electrochromic material rather than electrical signal, and thus the detection signal can be obtained by visualization without relying on complicated instrument. The entire test was performed with small fluorinated indium tin oxide electrodes modified with zinc oxide (ZnO) (a photocatalytic material) and Prussian blue (PB) (an electrochromic material). When photoinduced electrons produced by ZnO were injected into PB under light, the PB was reduced to Prussian white. The higher the concentration of TGEV, the more double-stranded DNA was produced after amplification. The amplified product produced greater impedance, and fewer electron was transferred, which affect the corresponding color change of PB. The sensing chip also showed highly sensitive response to TGEV, with the minimum limit of detection was determined to be 2.5 fg/μL. The sensing chip developed herein will provide a new avenue for DNA amplification detection by visualization.