Real-time dynamic single-molecule protein sequencing on an integrated semiconductor device.

Studies of the proteome would benefit greatly from methods to directly sequence and digitally quantify proteins and detect posttranslational modifications with single-molecule sensitivity. Here, we demonstrate single-molecule protein sequencing using a dynamic approach in which single peptides are probed in real time by a mixture of dye-labeled N-terminal amino acid recognizers and simultaneously cleaved by aminopeptidases. We annotate amino acids and identify the peptide sequence by measuring fluorescence intensity, lifetime, and binding kinetics on an integrated semiconductor chip. Our results demonstrate the kinetic principles that allow recognizers to identify multiple amino acids in an information-rich manner that enables discrimination of single amino acid substitutions and posttranslational modifications. With further development, we anticipate that this approach will offer a sensitive, scalable, and accessible platform for single-molecule proteomic studies and applications.

Spectroscopy and applications of the 3 3Σ+ electronic state of 39K85Rb.

We report new results on the spectroscopy of the 3 (3)Σ(+) electronic state of (39)K(85)Rb. The observations are based on resonance-enhanced multiphoton ionization of ultracold KRb molecules starting in vibrational levels v'' = 18-23 of the a (3)Σ(+) state and ionized via the intermediate 3 (3)Σ(+) state. The a-state ultracold molecules are formed by photoassociation of ultracold (39)K and (85)Rb atoms to the 3(0(+)) state of KRb followed by spontaneous emission. We discuss the potential applications of this state to future experiments, as a pathway for populating the lowest vibrational levels of the a state as well as the X state.

Spectroscopy of the double minimum 3 (3)ΠΩ electronic state of 39K85Rb.

We report the observation and analysis of the 3 (3)ΠΩ double-minimum electronic excited state of (39)K(85)Rb. The spin-orbit components (0(+), 0(-), 1, and 2) of this state are investigated based on potentials developed from the available ab initio potential curves. We have assigned the vibrational levels v' = 2-11 of the 3 (3)Π1,2 potentials and v' = 2-12 of the 3(3)Π0(+/-) potential. We compare our experimental observations of the 3 (3)ΠΩ state with predictions based on theoretical potentials. The observations are based on resonance enhanced multiphoton ionization of ultracold KRb in vibrational levels v" = 14-25 of the a (3)Σ(+) state. These a-state ultracold molecules are formed by photoassociation of ultracold (39)K and (85)Rb atoms to the 5(1) state of KRb followed by spontaneous emission to the a state.