Emission spectra, luminescent probes

An illustration of two spectroscopic techniques used to probe DNA. (A) The variation in luminescence characteristics of Ruiphenls with DNA binding. Shown is the emission spectrum of free Ruiphenls " (-----------), A-Ru(phen)3 + in the presence of DNA (.), and... 

Even larger probes of bent and kinked DNA are 40 A photoluminescent mineral colloidal particles of CdS [247-253]. These nanoparticles are approximately the size of proteins and can be made in a variety of sizes ( 20-100 A) and decorated with a variety of surface groups [267-279]. The emission spectrum of a nanoparticle solution depends on particle size and surface group synthetic procedures for CdS and other semiconductor nanoparticles have been developed so that the emission can be tuned throughout the visible spectrum and into the near infrared [267-279]. Moreover, the photoluminescence of CdS is sensitive to adsorbates [280-289], and thus these nanomaterials can function as luminescent chemical sensors. 

A MLC probe which intercalates Into double-helicsl DNA, [Ru(bpy)2(dppz)], where dppz is dipyrido-(3,2a 2, 3 -c]phenaziDB shown in Figure 20.14. This probe is quenched in water and is highly luminescent when bound to DNA. The emission spectrum of (Ru(bpy)2(dppz)] bound to calf thymus DNA is shown... 

The first sensor of that kind was presented by Sun et al. [48] who reported on a pH sensor based on the upconversion luminescence of NaYF4 Yb,Er nanorods (see inset Fig. 6b) that were embedded in a matrix of hydrogel along with the longwave absorbing pH probe (bromothymol blue BTB) that causes a pH dependent inner filter effect (Fig. 6a). The emission spectrum of the nanorods at NIR excitation and the pH dependent absorption spectrum of BTB for three pH values are shown in Fig. 6b. 

RET occurs via long-range dipole-dipole interactions and does not require direct molecular contact between the analyte and the probe. For RET to occur, a donor -acceptor system with spectral overlap is required, such that the emission spectrum of donor (D) overlaps with the absorption spectrum of acceptor (A). The acceptor may or may not be a lumophore. In RET sensors the presence of the analyte perturbs the electronic transitions of either the donor or acceptor in some way, so that the efficiency of the RET process is affected. Experimentally, RET shares many similarities with collisional quenching, typically resulting in a decrease the luminescence intensity and lifetime of the probe. Mechanistically, however, the processes are quite different and differ in both their concentration and distance dependencies. 

X 300 im diode mesas were defined by chlorine-based reactive ion etching (RIE). Pd/Au (3/200 nm) and Al/Au (30/200 nm) were used as fi-GaN and n-GaN contacts, respectively. The electrical and luminescence characteristics of the diode were measured by on-wafer probing of the devices. The I-V measurements were performed with a Hewlett-Packard 4155B semiconductor parameter analyzer. Relative optical power measurements under direct current (DC) conditions were obtained from the backside emission through the sapphire substrate onto a calibrated broad area Si photodiode. The emission spectrum and the optical power emission of the LEDs were measured as a function of drive currents. All measurements were carried out at room temperature. 

Until very recently, studies of the use of luminescent lanthanide complexes as biological probes concentrated on the use of terbium and europium complexes. These have emission lines in the visible region of the spectrum, and have long-lived (millisecond timescale) metal-centered emission. The first examples to be studied in detail were complexes of the Lehn cryptand (complexes (20) and (26) in Figure 7),48,50,88 whose luminescence properties have also been applied to bioassay (vide infra). In this case, the europium and terbium ions both have two water molecules... 

Texas Red hydrazide is a derivative of Texas Red sulfonyl chloride made by reaction with hydrazine (Invitrogen). The result is a sulfonyl hydrazine group on the No. 5 carbon position of the lower-ring structure of sulforhodamine 101. The intense Texas Red fluorophore has a QY that is inherently higher than either the tetramethylrhodamine or Lissamine rhodamine B derivatives of the basic rhodamine molecule. Texas Red s luminescence is shifted maximally into the red region of the spectrum, and its emission peak only minimally overlaps with that of fluorescein. This makes derivatives of this fluorescent probe among the best choices of labels for use in double-staining techniques. 

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