Freeze-Driven Synthesis of DNA Hairpin-Conjugated Gold Nanoparticle Biosensors for Dual-Mode Detection.

Freeze-based immobilization of deoxyribonucleic acid (DNA) oligonucleotides on gold nanoparticles (AuNPs) is highly efficient for single-stranded oligonucleotides but typically does not accommodate structures such as snap-cooled DNA hairpins (Sc-HPs) and snap-cooled molecular beacons (Sc-MBs) frequently used for biorecognition applications. Recognizing this limitation, we have developed a modified, freeze-based technique specifically designed to enable the adsorption of such hairpin oligonucleotides onto AuNP surfaces while ensuring that they retain their biosensing capabilities. Successful hairpin oligonucleotide conjugation of varying lengths to a wide range of AuNP diameters was corroborated by dynamic light scattering, ζ-potential, and UV-vis spectrophotometry. Moreover, we conducted a thorough evaluation of this modified method, confirming the retention of the sensing functions of Sc-HPs and Sc-MBs. This advancement not only offers a more efficient route for DNA hairpin conjugation but also elucidates the underlying biorecognition functions, with implications for broader applications in molecular diagnostics.

Evaluation of indirect sequence-specific magneto-extraction-aided LAMP for fluorescence and electrochemical SARS-CoV-2 nucleic acid detection.

Nucleic acid amplification tests (NAATs) such as quantitative real-time reverse transcriptase PCR (qRT-PCR) or isothermal NAATs (iNAATs) such as loop-mediated isothermal amplification (LAMP) require pure nucleic acid free of any polymerase inhibitors as its substrate. This in turn, warrants the use of spin-column mediated extraction with centralized high-speed centrifuges. Additionally, the utilization of centralized real-time fluorescence readout and TaqMan-like molecular probes in qRT-PCR and real-time LAMP add cost and restrict their deployment. To circumvent these disadvantages, we report a novel sample-to-answer workflow comprising an indirect sequence-specific magneto-extraction (also referred to as magnetocapture, magneto-preconcentration, or magneto-enrichment) for detecting SARS-CoV-2 nucleic acid. It was followed by in situ fluorescence or electrochemical LAMP. After in silico validation of the approach's sequence selectivity against SARS-CoV-2 variants of concern, the comparative performance of indirect and direct magnetocapture in detecting SARS-CoV-2 nucleic acid in the presence of excess host nucleic acid or serum was probed. After proven superior, the sensitivity of the indirect sequence-specific magnetocapture in conjunction with electrochemical LAMP was investigated. In each case, its sensitivity was assessed through the detection of clinically relevant 102 and 103 copies of target nucleic acid. Overall, a highly specific nucleic acid detection method was established that can be accommodated for either centralized real-time SYBR-based fluorescence LAMP or portable electrochemical LAMP.

A batch processed titanium-vanadium oxide nanocomposite based solid-state electrochemical sensor for zeptomolar nucleic acid detection.

Approaching a nucleic acid amplification test (NAAT) based diagnosis of a pathogen from an electrochemistry pathway is a relatively economical, decentralized, and yet highly sensitive route. This work aimed to construct an electrochemical biosensor with a 2-electrode geometry using a transition metal oxide (TMO) based sensing layer. A series of batch-processed TiO2-V2O5 (TVO) nanocomposite-based electrodes were fabricated to probe their electrochemical performance and attain a highly sensitive dual-electrode electrochemical sensor (DEES) compared to pristine V2O5. The XRD analysis of the electrodes confirmed the formation of a nanocomposite, while the XPS analysis correlated the formation of oxygen vacancies with improved electrical conduction measured via EIS and I-V characterization. Furthermore, the work demonstrated the application of the optimized electrode in electrochemical detection of end-point loop-mediated isothermal amplification (LAMP) readout for 101-104 copies (0.1 zeptomoles to 0.1 attomoles) of SARS-CoV-2 RNA dependent RNA polymerase (RdRp) plasmid DNA and in vitro transcribed RNA in an aqueous solution. The device achieved a limit of detection as low as 2.5 and 0.25 copies per µL for plasmid DNA and in vitro transcribed RNA, respectively. The DEES was able to successfully detect in situ LAMP performed on magneto-extracted SARS-CoV-2 plasmid and RNA from (a) an aqueous solution, (b) a sample spiked with excess human genomic DNA, and (c) a serum-spiked sample. The DEES results were then compared with those of real-time fluorescence and commercially available screen-printed electrodes (SPEs).

Limited-resource preparable chitosan magnetic particles for extracting amplification-ready nucleic acid from complex biofluids.

Extraction and concentration of pure nucleic acid from complex biofluids are the prerequisite for nucleic acid amplification test (NAAT) applications in pathogen detection, biowarfare prevention, and genetic diseases. However, conventional spin-column mediated nucleic acid extraction is constricted by the requirement for costly power-intensive centralized lab infrastructure, making it unsuitable for limited-resource settings. Significant progress in lab-on-a-chip devices or cartridges (e.g., Cepheid GeneXpert®) that integrate nucleic acid extraction and amplification has been made, but these approaches either require additional equipment or are costly. Similarly, their complexities make them difficult to fabricate in low-resource settings by the end-user themselves. The application of magnetic particles such as silica-coated iron oxide beads for nucleic acid extraction is relatively instrument-free, rapid, user-friendly, and amenable to automation. But, they rely on hazardous chaotropic salt chemistry and ethanol desalting that could limit their efficacy for downstream NAATs. Recent advances in several types of novel material (e.g., polyamine) coated magnetic bead-based chaotropic salt-free extraction methods offer a possible solution to this problem. However, these materials also involve multistep synthesis impermissible in limited-resource settings. To offer a possible instrument-free magnetic particle-based nucleic acid extraction doable at limited-resource settings, we investigated the nucleic acid capture ability of two chitosan-coated magnetic particles that are preparable by minimally trained personnel using only a water bath and a magnetic stirrer within 6-8 h. We quantitatively probed the efficiency of the passive (without any electrical shaking or vortex-aided) DNA magnetocapture (i.e., binding to chitosan magnetic particles, physical separation from its sample of origin, and release from the particles) using UV260. To explore their suitability towards clinically relevant sensitive downstream NAATs, 100-1000 copies (i.e., in the order of zeptomole) of Escherichia coli (E. coli) or human genomic DNA from aqueous solution, crude cell lysate, and fetal bovine serum were extracted by them and then successfully detected using quantitative real-time loop-mediated isothermal amplification (LAMP) or real-time polymerase chain reaction (PCR). Alongside, their suitability with gel-based LAMP, colorimetric LAMP, and in situ (on beads) LAMP was also probed. The required optimization of the amplification methods has been discussed. Overall, the turnaround time for the magnetocapture combined with NAAT was 1.5-2 h and is thus expected to aid in rapid clinical decision making. With the ease of preparation, reproducibility, and compatibility with downstream NAATs, we anticipate that these magnetic particles would facilitate the expansion and decentralization of nucleic acid-based diagnosis for limited-resource settings.

Design, synthesis and biological evaluation of a novel library of antimitotic C2-aroyl/arylimino tryptamine derivatives that are also potent inhibitors of indoleamine-2, 3-dioxygenase (IDO).

A novel library of C2-substituted tryptamines (based on diverse C2-aroyl/arylimino indoles and indole-diketopiperazine hybrids) possessing antimitotic properties were designed, synthesized and screened for their inhibitory activity against tubulin polymerization, and against proliferation of A549 lung cancer, HeLa cervical cancer, MCF7 breast cancer and HePG2 liver cancer cell lines. The design of molecules were inspired from known antimitotic compounds and natural products. The molecular docking of the designed compounds indicated that they bind to the colchicin binding site of tubulin. They were synthesized by a unique iodine catalysed oxidative ring opening reaction of 1-aryltetrahydro-ß-carbolines. Among the compounds synthesized quite a few compounds induced cytotoxicity on the cancer cells by disrupting the tubulin polymerization. They were found to be non-toxic for healthy cells. Immuno Fluorescence study for the most active molecules (between ~6 µM concentration) against A549 and HeLa cells demonstrated complete disruption and shrinkage of the microtubule structures. These compounds also inhibited indoleamine-2, 3-dioxygenase with low micromolar IC50.

Spiro[pyrrolidine-3, 3´-oxindole] as potent anti-breast cancer compounds: Their design, synthesis, biological evaluation and cellular target identification.

The spiro[pyrrolidine-3, 3´-oxindole] moiety is present as a core in number of alkaloids with substantial biological activities. Here in we report design and synthesis of a library of compounds bearing spiro[pyrrolidine-3, 3´-oxindole] motifs that demonstrated exceptional inhibitory activity against the proliferation of MCF-7 breast cancer cells. The synthesis involved a one pot Pictet Spengler-Oxidative ring contraction of tryptamine to the desired scaffolds and occurred in 1:1 THF and water with catalytic trifluoroacetic acid and stoichiometric N-bromosuccinimide as an oxidant. Phenotypic profiling indicated that these molecules induce apoptotic cell death in MCF-7 cells. Target deconvolution with most potent compound 5l from the library, using chemical proteomics indicated histone deacetylase 2 (HDAC2) and prohibitin 2 as the potential cellular binding partners. Molecular docking of 5l with HDAC2 provided insights pertinent to putative binding interactions.