Spectrochimica Acta Part A 60 (2004) 959–964 Determination of nucleic acids with tetra-(N-hexadecylpyridiniumyl) porphyrin sensitized by cetyltrimethylammonium bromide (CTMAB) using a Rayleigh light-scattering technique Changqing Zhu ∗ , Shujuan Zhuo, Yongxin Li, Lun Wang, Danhua Zhao, Jinlong Chen, Yuqin Wu College of Chemistry and Materials Science, Anhui Normal Unversity, Wuhu 241000, PR China Received 15 May 2003; accepted 11 July 2003 Abstract Using a common spectrofluorometer to measure the intensity of Rayleigh light-scattering (RLS), a method for determination of nucleic acids has been developed. At pH 10.24 and ionic strength 0.01 mol l -1 (NaCl), the Rayleigh light-scattering of the tetra-(N-hexadecylpyridiniumyl) porphyrin (TC 16 PyP) is greatly enhanced by nucleic acids in the presence of cetyltrimethylammonium bromide (CTMAB), with the scattering peak located at 311.8 nm. The enhanced RLS intensity is in proportion to the concentration of calf thymus DNA (ctDNA) in the range 0.2–6.0 g ml -1 and to that of fish sperm DNA (fsDNA) in the range 0.05–3.0 g ml -1 . The limits of detection are 0.016 g ml -1 for calf thymus DNA and 0.023 g ml -1 for fish sperm DNA when the concentration of TPP was chosen 2.0 × 10 -6 mol l -1 . Four synthetic samples were determined satisfactorily. © 2003 Elsevier B.V. All rights reserved. Keywords: Tetra-(N-hexadecylpyridiniumyl) porphyrin (TC 16 PyP); Rayleigh light-scattering; Nucleic acids; Cetyltrimethylammonium bromide (CTMAB) 1. Introduction The quantitative analysis of nucleic acids is very impor- tant because it can be used as a reference for measurements of other components in biological fluids and genetic diag- nosis. Several methods have been reported to determine the content of nucleic acids in samples, such as spectrophoto- metric methods [1,2], fluorimetry [3–8], etc. But in recent years, Rayleigh light-scattering (RLS) technique has been extensively studied and applied to nucleic assay. Rayleigh scattering is a light-scattering phenomenon that electromagnetic radiation and material act each other and generate elastic collisions. According to the macroscopic fluctuation theory, the Rayleigh scattering law is obeyed, namely I ∝ 1/λ 4 [9], for the light scattering of the molecu- lar particles 20-fold smaller than the wavelength of the inci- dent beam. However, if the wavelength of the incident beam is close to that of the absorption band of the molecular parti- ∗ Corresponding author. Fax: +86-553-386-9303. E-mail address: zhucq625@163.com (C. Zhu). cles which exist as aggregates, Rayleigh scattering will devi- ate from the law and the intensity of some wavelengths will rapidly increase. This phenomenon is called resonance light scattering (RLS), or resonance enhanced Rayleigh scatter- ing, or resonance Rayleigh scattering. By using a common spectrofluorometer to measure the RLS, Pasternack and coworkers [10,11] studied the aggre- gations of porphyrines. Later on, Huang and co-workers discovered that by using the enhanced RLS intensity, trace amounts of nucleic acids [12,13] and protein [14] in syn- thetic and practical samples could be sensitively determined. The aggregation of porphyrines in presence of protein [15], the formation of the suprahelical helixes of nucleic acids, and the long range assembly of organic dyes on the surface of nucleic acids [16,17] have been studied. Up to now, the RLS technique has become a new, high sensitive technique for determining and researching biological macromolecules. Porphyrin is an easy available biological dye, which has applied in spectroscopy [18,19], chemical sensor [20], opti- cal absorption [21], fluorescence [22,23] and light scattering [24], etc. Porphyrin complexes, such as Mn(III), Fe(III), Zn(II) and Sn(IV) complexes of porphyrin [19,21,25], 1386-1425/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1386-1425(03)00325-1