TY - JOUR A1 - Geissler, Daniel A1 - Stufler, Stefan A1 - Löhmannsröben, Hans-Gerd A1 - Hildebrandt, Niko T1 - Six-color time-resolved forster resonance energy transfer for ultrasensitive multiplexed biosensing JF - Journal of the American Chemical Society N2 - Simultaneous monitoring of multiple molecular interactions and multiplexed detection of several diagnostic biomarkers at very low concentrations have become important issues in advanced biological and chemical sensing. Here we present an optically multiplexed six-color Forster resonance energy transfer (FRET) biosensor for simultaneous monitoring of five different individual binding events. We combined simultaneous FRET from one Tb complex to five different organic dyes measured in a filter-based time-resolved detection format with a sophisticated spectral crosstalk correction, which results in very efficient background suppression. The advantages and robustness of the multiplexed FRET sensor were exemplified by analyzing a 15-component lung cancer immunoassay involving 10 different antibodies and five different tumor markers in a single 50 mu L human serum sample. The multiplexed biosensor offers clinically relevant detection limits in the low picomolar (ng/mL) concentration range for all five markers, thus providing an effective early screening tool for lung cancer with the possibility of distinguishing small-cell from non-small-cell lung carcinoma. This novel technology will open new doors for multiple biomarker diagnostics as well as multiplexed real-time imaging and spectroscopy. Y1 - 2013 U6 - https://doi.org/10.1021/ja310317n SN - 0002-7863 VL - 135 IS - 3 SP - 1102 EP - 1109 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Harma, Harri A1 - Pihlasalo, Sari A1 - Cywinski, Piotr J. A1 - Mikkonen, Piia A1 - Hammann, Tommy A1 - Löhmannsröben, Hans-Gerd A1 - Hanninen, Pekka T1 - Protein quantification using resonance energy transfer between donor nanoparticles and acceptor quantum dots JF - Analytical chemistry N2 - A homogeneous time-resolved luminescence resonance energy transfer (TR-LRET) assay has been developed to quantify proteins. The competitive assay is based on resonance energy transfer (RET) between two luminescent nanosized particles. Polystyrene nanoparticles loaded with Eu3+ chelates (EuNPs) act as donors, while protein-coated quantum dots (QDs), either CdSe/ZnS emitting at 655 nm (QD655-strep) or CdSeTe/ZnS with emission wavelength at 705 nm (QD705-strep), are acceptors. In the absence of analyte protein, in our case bovine serum albumin (BSA), the protein-coated QDs bind nonspecifically to the EuNPs, leading to RET. In the presence of analyte proteins, the binding of the QDs to the EuNPs is prevented and the RET signal decreases. RET from the EuNPs to the QDs was confirmed and characterized with steady-state and time-resolved luminescence spectroscopy. In accordance with the Forster theory, the approximate average donor acceptor distance is around 15 nm at RET efficiencies, equal to 15% for QD655 and 13% for QD705 acceptor, respectively. The limits of detection are below 10 ng of BSA with less than a 10% average coefficient of variation. The assay sensitivity is improved, when compared to the most sensitive commercial methods. The presented mix-and-measure method has potential to be implemented into routine protein quantification in biological laboratories. Y1 - 2013 U6 - https://doi.org/10.1021/ac303586n SN - 0003-2700 VL - 85 IS - 5 SP - 2921 EP - 2926 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Eich, Susanne A1 - Schmälzlin, Elmar A1 - Löhmannsröben, Hans-Gerd T1 - Distributed fiber optical sensing of Oxygen with optical time domain reflectometry JF - Sensors N2 - In many biological and environmental applications spatially resolved sensing of molecular oxygen is desirable. A powerful tool for distributed measurements is optical time domain reflectometry (OTDR) which is often used in the field of telecommunications. We combine this technique with a novel optical oxygen sensor dye, triangular-[4] phenylene (TP), immobilized in a polymer matrix. The TP luminescence decay time is 86 ns. The short decay time of the sensor dye is suitable to achieve a spatial resolution of some meters. In this paper we present the development and characterization of a reflectometer in the UV range of the electromagnetic spectrum as well as optical oxygen sensing with different fiber arrangements. KW - OTDR KW - optical sensing KW - molecular oxygen KW - triangular-[4] phenylene Y1 - 2013 U6 - https://doi.org/10.3390/s130607170 SN - 1424-8220 VL - 13 IS - 6 SP - 7170 EP - 7183 PB - MDPI CY - Basel ER - TY - JOUR A1 - Riebe, Daniel A1 - Laudien, Robert A1 - Brendler, Christian A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd T1 - Laser ionization of H2S and ion-molecule reactions of H3S+ in laser-based ion mobility spectrometry and drift cell time-of-flight mass spectrometry JF - Analytical & bioanalytical chemistry N2 - The detection of hydrogen sulfide (H2S) by 2 + 1 resonance-enhanced multi-photon ionization (REMPI) and the application of H2S as a laser dopant for the detection of polar compounds in laser ion mobility (IM) spectrometry at atmospheric pressure were investigated. Underlying ionization mechanisms were elucidated by additional studies employing a drift cell interfaced to a time-of-flight mass spectrometer. Depending on the pressure, the primary ions H2S+, HS+, S+, and secondary ions, such as H3S+, were observed. The 2 + 1 REMPI spectrum of H2S near lambda = 302.5 nm was recorded at atmospheric pressure. Furthermore, the limit of detection and the linear range were established. In the second part of the work, H2S was investigated as an H2O analogous laser dopant for the ionization of polar substances by proton transfer. H2S exhibits a proton affinity (PA) similar to that of H2O, but a significantly lower ionization energy facilitating laser ionization. Ion-molecule reactions (IMR) of H3S+ with a variety of polar substances with PA between 754.6 and 841.6 kJ/mol were investigated. Representatives of different compound classes, including alcohols, ketones, esters, and nitroaromatics were analyzed. The IM spectra resulting from IMR of H3S+ and H3O+ with these substances are similar in structure, i.e., protonated monomer and dimer ion peaks are found depending on the analyte concentration. KW - Ion mobility spectrometry KW - Mass spectrometry KW - REMPI KW - Hydrogen sulfide KW - Proton transfer reaction Y1 - 2013 U6 - https://doi.org/10.1007/s00216-013-7186-5 SN - 1618-2642 VL - 405 IS - 22 SP - 7031 EP - 7039 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Brendler, Christian A1 - Riebe, Daniel A1 - Ritschel, Thomas A1 - Beitz, Toralf A1 - Löhmannsröben, Hans-Gerd T1 - Investigation of neuroleptics and other aromatic compounds by laser-based ion mobility mass spectrometry JF - Analytical & bioanalytical chemistry N2 - Laser-based ion mobility (IM) spectrometry was used for the detection of neuroleptics and PAH. A gas chromatograph was connected to the IM spectrometer in order to investigate compounds with low vapour pressure. The substances were ionized by resonant two-photon ionization at the wavelengths lambda = 213 and 266 nm and pulse energies between 50 and 300 mu J. Ion mobilities, linear ranges, limits of detection and response factors are reported. Limits of detection for the substances are in the range of 1-50 fmol. Additionally, the mechanism of laser ionization at atmospheric pressure was investigated. First, the primary product ions were determined by a laser-based time-of-flight mass spectrometer with effusive sample introduction. Then, a combination of a laser-based IM spectrometer and an ion trap mass spectrometer was developed and characterized to elucidate secondary ion-molecule reactions that can occur at atmospheric pressure. Some substances, namely naphthalene, anthracene, promazine and thioridazine, could be detected as primary ions (radical cations), while other substances, in particular acridine, phenothiazine and chlorprothixene, are detected as secondary ions (protonated molecules). The results are interpreted on the basis of quantum chemical calculations, and an ionization mechanism is proposed. KW - Ion mobility spectrometry KW - Mass spectrometry KW - Gas chromatography KW - Laser ionization KW - REMPI KW - Neuroleptics Y1 - 2013 U6 - https://doi.org/10.1007/s00216-012-6654-7 SN - 1618-2642 VL - 405 IS - 22 SP - 7019 EP - 7029 PB - Springer CY - Heidelberg ER -