Biomedical subjects

J S Lundgren

Publications and source records attributed to J S Lundgren.

3 recordsLinked to original sources

PubMed2000

A liquid crystal pixel array for signal discrimination in array biosensors.

A new optical design uses a liquid crystal pixel array (LCPA) to discriminate multiple fluorescence signals on a two-dimensional biosensor array. The LCPA can selectively control the transmission of fluorescence generated from multiple biosensing elements on a planar waveguide. This device sequentially acquires the fluorescence data from the substrate by making multiple individual measurements of the sensing elements on the waveguide. The biosensing elements are patterned according to the pixel layout of the LCPA and optically aligned so that each electronically driven pixel can either transmit or filter out the fluorescence signal as specified by the user. The primary advantage of this system is that a single detection channel (i.e. photomultiplier tube (PMT)) can be used to measure multiple fluorescence signals from a two-dimensional substrate while the LCPA provides for spatial resolution. We evaluate the performance of the LCPA by testing the optical homogeneity of the liquid crystal pixels and linear dynamic range for transmitting light. The LCPA is also used with well-developed biosensing chemistry modified for this optical format.

Biosensing Techniques↗

PubMed1999

A dynamical investigation of acrylodan-labeled mutant phosphate binding protein.

The static and dynamical behavior of a fluorescently labeled mutant of the Escherichia coli periplasmic phosphate binding protein (PBP) was investigated through steady-state and time-resolved fluorescence spectroscopy. As a means of developing a biorecognition element for inorganic phosphate (P(i)), alanine-197 of PBP was replaced with a cysteine. This site was then labeled with an environmentally sensitive fluorophore. The fluorescence emission of the mutant PBP labeled with acrylodan (MPBP-AC) proved to be sensitive to micromolar concentrations of P(i), as indicated by a 50% increase in the steady-state emission intensity. Steady-state results indicated that the labeling protocol was specific for cys-197 only and did not label the wild-type PBP; thus, a site-selective labeling protocol was developed. Time-resolved measurements were used to determine the influence of the dynamics of MPBP-AC on the process of signal transduction. Time-resolved anisotropy measurements revealed that rotational dynamics were best described by a model with two independent motions: the global motion of the protein and the local motion of the acrylodan probe. The rates of both global and local rotational reorientation of MPBP-AC were faster when the protein was P(i)-bound rather than P(i)-free. This was a result of structural changes involving or surrounding both the P(i)-binding site (global changes) and the residues in near proximity to the fluorescent reporter group (local changes). Recovery of the semiangle (theta) indicated that local structural changes in MPBP-AC took place when P(i) was bound to the protein. Acrylodan gained mobility when MPBP-AC bound P(i), as indicated by the fact that theta increased by approximately 5 degrees. In addition, dynamic quenching measurements confirmed that structural changes occurred locally near the cys-197. Acrylodan became more accessible to iodide when MPBP-AC bound P(i), as demonstrated by the 35% increase in the value of the bimolecular quenching constant.

2-Naphthylamine↗

PubMed1995

Dynamics of acrylodan-labeled bovine and human serum albumin sequestered within aerosol-OT reverse micelles.

We investigate the effects of hydration on acrylodan-labeled bovine and human serum albumin (BSA-Ac and HSA-Ac) in aerosol-OT (AOT) reverse micelles solubilized in n-heptane. Time-resolved fluorescence intensity decay experiments reveal a dipolar relaxation process surrounding the acrylodan cybotactic region. This process is best described by a two-term rate law wherein the average relaxation increases with increased hydration. However, the actual rate constants describing the relaxation process either remain unchanged or actually decrease with increased hydration. The results illustrate that the fractional contribution associated with the individual relaxation pathways causes the observed changes in relaxation dynamics. The recovered rotational reorientation dynamics of the acrylodan residue are also affected by the extent of protein hydration. As hydration is increased, the semiangle through which the acrylodan residue precesses increases by 10 degrees for both protein systems. Interestingly, the recovered semiangles for the native proteins equal those recovered at lower hydration when the proteins are sequestered within the AOT reverse micelle. These results demonstrate the importance of hydration on protein behavior in environments where water is limited (e.g., biosensor interfaces and sol--gel-derived biocomposites).

2-Naphthylamine↗