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Modifications of genomic DNA may change gene expression and cause adverse health effects. Here we for the first time demonstrate a particle counting immunoassay for rapid and sensitive detection of DNA modifications using benzo[a]pyrenediol epoxide (BPDE)--DNA adducts as an example. The BPDE-adducted DNA is specifically captured by immunomagnetic particles and then isolated from unmodified DNA by applying an external magnetic field. By taking advantage of the fluorescence signal amplification through multiple labeling of captured DNA by OliGreen dye, the captured BPDE--DNA adducts can be quantified by particle counting from fluorescence imaging. This clearly demonstrates that the number of fluorescently countable particles is proportional to the modification content in genomic DNA. It is interesting to note that the background fluorescence signal caused by nonspecific adsorption of OliGreen dye can be more effectively quenched than that induced by the binding of OliGreen dye to ssDNA, allowing for significant reduction in the background fluorescence and further enhancing the detection sensitivity. The developed method can detect trace BPDE--DNA adducts as low as 180 fM in the presence of I billion times more normal nucleotides in genomic DNA and has a dynamic range over 4 orders of magnitude. By using anti-5-methylcytosine antibody, the method is extended to the detection of global DNA methytation. With high sensitivity and specificity, this rapid and easy-to-perform analytical method for DNA modifications shows a broad spectrum of potential applications in genotexical and epigenetic analysis. 10.1021/ac102416f

A capillary monolithic bioreactor of snake venom phosphodiesterase (SVP) was constructed to generate different single-nucleotide mass ladders of oligodeoxynucleotides for mass spectrometry (MS)-based sequencing by immobilization. The immobilization of SVP in the porous silica monolith significantly enhances its stability for prolonged and repeated applications. The constructed capillary bioreactor has the advantages of handling (sub)microliter DNA samples and having good permeability. Benefiting from its good permeability, DNA solutions can be directly injected into the sequential digestion bioreactor simply by hand pushing or a low-pressure microinjection pump. Moreover, the immobilization of SVP facilitates the elimination or repression of the metal adducts of oligodeoxynucleotides, improving the analytical performance of MS sequencing. By the application of capillary bioreactor of immobilized SVP, the sequence-specific modification of single-stranded oligodeoxynucleotide induced by a ubiquitous pollutant acrolein (Acr) was identified, demonstrating its promising applications in identification of sequence-specific damage, which may further our understanding of DNA damage caused mutagenesis.