Towards maintenance-free biosensors for hundreds of bind/release cycles.

A single aptamer bioreceptor layer was formed using a common streptavidin-biotin immobilization strategy and employed for 100-365 bind/release cycles. Chemically induced aptamer unfolding and release of its bound target was accomplished using alkaline solutions with high salt concentrations or deionized (DI) water. The use of DI water scavenged from the ambient atmosphere represents a first step towards maintenance-free biosensors that do not require the storage of liquid reagents. The aptamer binding affinity was determined by surface plasmon resonance and found to be almost constant over 100-365 bind/release cycles with a variation of less than 5% relative standard deviation. This reversible operation of biosensors based on immobilized aptamers without storage of liquid reagents introduces a conceptually new perspective in biosensing. Such new biosensing capability will be important for distributed sensor networks, sensors in resource-limited settings, and wearable sensor applications.

Emerging understanding of multiscale tumor heterogeneity.

Cancer is a multifaceted disease characterized by heterogeneous genetic alterations and cellular metabolism, at the organ, tissue, and cellular level. Key features of cancer heterogeneity are summarized by 10 acquired capabilities, which govern malignant transformation and progression of invasive tumors. The relative contribution of these hallmark features to the disease process varies between cancers. At the DNA and cellular level, germ-line and somatic gene mutations are found across all cancer types, causing abnormal protein production, cell behavior, and growth. The tumor microenvironment and its individual components (immune cells, fibroblasts, collagen, and blood vessels) can also facilitate or restrict tumor growth and metastasis. Oncology research is currently in the midst of a tremendous surge of comprehension of these disease mechanisms. This will lead not only to novel drug targets but also to new challenges in drug discovery. Integrated, multi-omic, multiplexed technologies are essential tools in the quest to understand all of the various cellular changes involved in tumorigenesis. This review examines features of cancer heterogeneity and discusses how multiplexed technologies can facilitate a more comprehensive understanding of these features.

Theoretical limit of localized surface plasmon resonance sensitivity to local refractive index change and its comparison to conventional surface plasmon resonance sensor.

In this paper, the theoretical sensitivity limit of the localized surface plasmon resonance (LSPR) to the surrounding dielectric environment is discussed. The presented theoretical analysis of the LSPR phenomenon is based on perturbation theory. Derived results can be further simplified assuming quasistatic limit. The developed theory shows that LSPR has a detection capability limit independent of the particle shape or arrangement. For a given structure, sensitivity is directly proportional to the resonance wavelength and depends on the fraction of the electromagnetic energy confined within the sensing volume. This fraction is always less than unity; therefore, one should not expect to find an optimized nanofeature geometry with a dramatic increase in sensitivity at a given wavelength. All theoretical results are supported by finite-difference time-domain calculations for gold nanoparticles of different geometries (rings, split rings, paired rings, and ring sandwiches). Numerical sensitivity calculations based on the shift of the extinction peak are in good agreement with values estimated by perturbation theory. Numerical analysis shows that, for thin (≤10 nm) analyte layers, sensitivity of the LSPR is comparable with a traditional surface plasmon resonance sensor and LSPR has the potential to be significantly less sensitive to temperature fluctuations.

Simultaneous optimization of monolayer formation factors, including temperature, to significantly improve nucleic acid hybridization efficiency on gold substrates.

Past literature investigations have optimized various single factors used in the formation of thiolated, single stranded DNA (ss-DNA) monolayers on gold. In this study a more comprehensive approach is taken, where a design of experiment (DOE) is employed to simultaneously optimize all of the factors involved in construction of the capture monolayer used in a fluorescence-based hybridization assay. Statistical analysis of the fluorescent intensities resulting from the DOE provides empirical evidence for the importance and the optimal levels of traditional and novel factors included in this investigation. We report on the statistical importance of a novel factor, temperature of the system during monolayer formation of the capture molecule and lateral spacer molecule, and how proper usage of this temperature factor increased the hybridization signal 50%. An initial theory of how the physical factor of heat is mechanistically supplementing the function of the lateral spacer molecule is provided.

Improved specific biodetection with ion trap mobility spectrometry (ITMS): a 10-min, multiplexed, immunomagnetic ELISA.

Enabling trace chemical detection equipment utilized in the field to transduce a biodetection assay would be advantageous from a logistics, training, and maintenance standpoint. Described herein is an assay design that uses an unmodified, commercial off-the-shelf (COTS) ion trap mobility spectrometer to analyze an immunomagnetic enzyme-linked immunosorbant assay (ELISA). The assay, which uses undetectable enzymatic substrates and ELISA-generated detectable products, was optimized to quantitatively report the amount of target in the sample. Optimization of this ELISA design retained the assay specificity and detection limit (approximately 10(3) E. coli per assay) while decreasing the number of user steps and reducing the assay time to 10 min (>9-fold decrease as compared to past studies). Also discussed are previously undescribed, independent substrate/enzyme/product combinations used in the immunomagnetic ELISA. These discoveries allow for the possibility of a quantitative, multiplexed, 10-min assay that is analyzed by the ion trap mobility spectrometer trace chemical detector.

Matrix effects by specific buffer components in the analysis of metabolites with ion trap mobility spectrometry.

The impact of buffer conditions on the ion trap mobility spectrometer (ITMS) signal is investigated through a series of statistically driven design of experiments (DOEs). A growing number of new ion mobility spectrometry (IMS) and ITMS applications are being performed with a physiological sample matrix, which is vastly different from the particulate and vapor matrixes that have been traditionally analyzed. Currently, there have been no efforts to globally examine the possibility of matrix suppression or enhancement of the IMS signal by these various components within physiological matrixes. This investigation consists of an effort to gauge the effects of common physiological buffer components and concentrations on two analytes of interest for ITMS analysis: o-nitrophenol and ephedrine. We show that, among the factors investigated, for a specific analyte and instrumental detection mode (i.e., negative/positive) the solution pH, presence of a protein, the buffer identity, and buffer concentration should be considered as they will enhance or suppress the ITMS signal while factors such as surfactant and salt concentration may play less of a role in impacting detectable ITMS signal. These observations are supported through statistical analysis of the DOE-derived data set.

Nanoparticle coding: size-based assays using atomic force microscopy.

Described herein is a novel strategy for the construction and interrogation of an assay platform based on (1) the size encoding of labeled nanoparticles; (2) the high imaging resolution of atomic force microscopy; and (3) evaporatively driven self-assembly of dense nanoparticle layers. This strategy employs two different sized nanoparticles that couple in the presence of a target analyte. In this example, one set of particles is a few hundred nanometers in size and acts as a capture substrate, while a second set of smaller particles serve as the analyte label. Thus, by forming an evaporatively assembled layer from a mixture of the two particle dispersions, the imaged size of the smaller particles when bound to the larger capture particles identifies the presence of the analyte. This letter demonstrates the feasibility of our bar-code strategy by concept tests using the binding specificity of biotin-modified silica nanoparticles (300-nm diameter) with streptavidin-labeled gold nanoparticles (10-nm diameter). The potential to extensively multiplex this assay strategy is briefly discussed.

Thin films of block copolymer blends for enhanced performance of acoustic wave-based chemical sensors.

The performance of quartz crystal oscillator-based volatile organic compound (VOC) sensors has been enhanced by using coatings made from poly(styrene-block-ethylene-co-butylene-block-styrene) block copolymers blended with resins and homopolymers. Enhanced performance is characterized by a wider operational temperature range (-10 to +50 degrees C) over which the sensors displayed, concurrently, an analyte sensitivity of >0.2 Hz/ppm toluene, minimal energy loss (resistance <120 ohms), and response times of <20 min (time required to reach 90% of full response). Atomic force microscopy images are consistent with a process in which the additive associates with the polystyrene portions of the microphase-separated block copolymer. This association reinforces the rigidity of the polystyrene network while allowing the rapid uptake of VOCs by the softer polyethylene/butylene phase.