Some raw materials that have different places of production for the plant sources of the drugs Astragalus membranaceus and ginseng have been studied, based on their near-infrared reflectance spectra. The experimentally recorded spectra represent heavily ill-posed and highly correlative data sets. Three related methods, i.e. the Fisher linear discriminant analysis (FLDA), the ridge-type linear discriminant analysis (RLDA) and a newly proposed penalized ridge-type linear discriminant analysis (PRLDA), have been investigated. FLDA over-fits for the training objects of the two data sets to a high extent and is unstable for the predictive objects of the two data sets. RLDA shows obvious improvement in terms of over-fitting and unstability, but the stability for the predictive objects of the two data sets is too sensitive to their ridge-type penalized weights, tending to produce erroneous discrimination results. The proposed PRLDA can circumvent the two aforementioned problems with a large domain of penalized weights for correct discriminant analysis of the two data sets studied. The combination of the PRLDA method and near infrared reflectance spectroscopy can be adapted for the discrimination of the production places of plant sources of these drugs.

The approach for DNA detection was established by using a fluorescence resonance energy transfer (FRET) system, in which the energy donor was poly-diallyldimethylammonium chloride-protected quantum dots and the energy receptor was ethidium bromide (EB) inserting into the double stranded DNA. The concentration of the probe DNA, EB and NaCl was optimized. Under the optimized conditions, the FRET system has a stable signal and good reproducibility. The linear range is 7.7–61.6 nM with the correlation coefficient of 0.998 and the limit of detection is 7.7 nM. This method is simple and sensitive, and makes the label-free DNA detection come true.

The nanocomposites of poly-diallyldimethylammonium chloride (PDADMAC) and CdTe quantum dots (QDs) (i.e. QDs-PDADMAC nanocomposites) have been prepared based on electrostatic interaction and their fluorescence stability in aqueous solution has been investigated. MTT method (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide method) was used to study their cytotoxicity and A549 lung cancer cell as a model cell was also used to evaluate their cellular imaging. It was shown that the fluorescence stability of QDs-PDADMAC nanocomposites was much better than that of bare QDs both in aqueous solution and cell. Meanwhile, QDs-PDADMAC nanocomposites display very low cytotoxicity in the low concentrations and better staining ability compared with QDs. QDs-PDADMAC nanocomposites will have great advantage on the cell analysis detection and imaging.

Fluorescent nanoparticles with a novel structure suitable for detecting cancer cells in vitro and in vivo have been prepared. Firstly, a strong, hydrophilic, branched amino polymer was synthesized, and then it was chemically conjugated as much as possible with fluorescein (FAM) to further synthesize a hydrophobic FAM-branched polymer with strong fluorescence. Fluorescein polymer nanoparticles (FPNPs) were then prepared based on hydrophobic interactions of the as-synthesized FAM-branched polymers, and polyacrylic acids (PAAs) were crosslinked on the surface to cover FPNPs and then to prepare PAA surface-crosslinked FPNPs (paa-FPNPs). The as-prepared paa-FPNPs nanoparticles have a fluorescent “core-cover-type” rigid structure and a non-fluorescent flexible structure consisting of the residual chains of the surface-crosslinked PAAs. The paa-FPNPs have four excellent properties as follows: (1) small particle size, a narrow particle distribution and rich negative surface charge; (2) strong fluorescence resulting from the hydrophobic interaction-based aggregation of a large number of the fluorophores conjugated on the branched amino polymers, and from a thin-cover-based weak fluorescence shielding; (3) good protection of the embedded fluorophores against in vivo enzymatic hydrolysis, owing to the outer cover and the negative residual chains of PAAs; (4) weak steric hindrance of the nanoparticle-labeled aptamer recognizing a huge-size target cell. The prepared paa-FPNPs have both a strong fluorescence and a suitable nanoparticle structure for cell imaging. Based on the ligand aptamer labeled by paa-FPNP, this paper reports the sensitive in vitro imaging of cancer cells and long-life in vivo imaging of in situ tumors.