Microbiological intelligence: Simple constructs of hydrophobically functionalized gold nanoarticles and a conjugated polymer (poly(para‐phenyleneethynylene, PPE) are able to identify three different strains of E. coli in minutes. The negatively charged bacteria replace the negatively charged conjugated polymers from the positively charged gold nanoparticles (see scheme), differentially restoring the polymer fluorescence.

Rapid and effective differentiation between normal and cancer cells is an important challenge for the diagnosis and treatment of tumors. Here, we describe an array-based system for identification of normal and cancer cells based on a ''chemical nose/tongue'' approach that exploits subtle changes in the physicochemical nature of different cell surfaces. Their differential interactions with functionalized nanoparticles are transduced through displacement of a multivalent polymer fluorophore that is quenched when bound to the particle and fluorescent after release. Using this sensing strategy we can rapidly (minutes/seconds) and effectively distinguish (i) different cell types; (ii) normal, cancerous and metastatic human breast cells; and (iii) isogenic normal, cancerous and metastatic murine epithelial cell lines.fluorescence ͉ gold nanoparticle ͉ sensor ͉ conjugated polymer

Convenient, precise, and rapid protein sensing methods are of great importance in medical diagnostics and proteomics. 1 Widely used specific interaction-based sensing protocols (e.g., ELISA) require protein receptors of high affinity and specificity requiring the generation of pertinent protein receptors/ligands for multiprotein detection. 1 In this regard, sensor array approaches are attractive, using differential binding interactions that are selective rather than specific. 2 This "electronic nose/tongue" strategy provides highly versatile sensors. 3,4 Recently, this principle has been used for protein detection through either fluorescence quenching 5 or indicator displacement. 6 While these sensors have been effective, they feature high limits of detection, and only relatively small sets (4-5 proteins) were studied.Effective protein sensing requires efficient protein receptors and competent signal transducers. Water-soluble conjugated polymers with pendant-charged residues provide an excellent scaffold for sensor design. 7,8 These materials can bind protein surfaces through multivalent interactions. Moreover, their optical properties are sensitive to minor conformational or environmental changes, 7,9 enabling efficient signal transduction of the binding events. In this work, we use six functionalized poly(p-phenyleneethynylene)s (PPEs) 10 to build a protein sensor array (Figure 1). These highly fluorescent polymers possess various charge characteristics and molecular scales. Such structural features provide tremendous binding diversity upon interaction with protein analytes, generating distinct fluorescence response patterns for protein discrimination.We have chosen 17 proteins as the sensing targets (Table 1). These proteins possess diverse structural characteristics including metal/nonmetal-containing, molecular weight (MW), isoelectric point (pI), and UV absorbencies. Notably, many protein targets have comparable MW and pI values, thereby providing excellent objects for examining the differentiation ability of the PPE-based sensor array.In the sensing studies, the fluorescence of the polymer solution (100 nM, on the basis of number-averaged molecular weight) in phosphate buffered saline (PBS) was recorded before and after addition of protein analytes. The six polymers display substantial overlap in their absorption and emission spectra (Figure S1), allowing the same excitation wavelength (430 nm) and emission wavelength (465 nm) to be used for all polymers to expedite their analysis on the microplate reader. To facilitate the quantitative detection of proteins, we generated patterns at protein concentrations at a standard UV absorbance (A 280 ) 0.005), the lowest concentration for all proteins to induce substantial emission changes of the polymers. With this as the detection limit of the system, protein identification was readily achieved in combination of UV measurements (vide post). Besides metalloproteins, such as CytC, Fer, Hem,

Cationic monolayer-protected gold nanoparticles (AuNPs) with sizes of 6 or 2 nm interact with the cell membranes of Escherichia coli (Gram-) and Bacillus subtilis (Gram+), resulting in the formation of strikingly distinct AuNP surface aggregation patterns or lysis depending upon the size of the AuNPs. The aggregation phenomena were investigated by transmission electron microscopy and UV-vis spectroscopy. Upon proteolytic treatment of the bacteria, the distinct aggregation patterns disappeared.

A family of conjugated fluorescent polymers was used to create an array for cell sensing. Fluorescent conjugated polymers with pendant charged residues provided multivalent interactions with cell membranes, allowing the detection of subtle differences between different cell types on the basis of cell surface features. Highly reproducible characteristic patterns were obtained from different cell types as well as from isogenic cell lines, enabling the identification of the cell type as well differentiating between normal, cancerous, and metastatic isogenic cell types with high accuracy.

To explore molecular recognition of biomolecules in the complex environment of the extracellular matrix, we utilized two fluorescent poly(p-phenyleneethynylene)s bearing either cationic alkylammonium or negatively charged carboyxlate side chains. While incubation of live NIH 3T3 fibroblast cells with the cationic polymer yielded perinuclear punctate staining reminiscent of endocytotic vesicles, the carboxylated polymer revealed a characteristic filamentous staining pattern. Histochemical and immunofluorescence studies demonstrated that the anionic PPE selectively binds to fibronectin fibrils of the extracellular matrix. An in vitro binding study revealed a dissociation constant of approximately 100 nM for the fibronectin-polymer complex. Both polymers showed bright two-photon excited emission as well as low toxicity, rendering them well-suited for live cell imaging studies. The studies demonstrate that selective molecular recognition of biomolecules in the complex environment of the extracellular matrix can be achieved by means of nonspecific low-affinity polyvalent interactions.

Using the Langmuir-Blodgett (LB) technique, a poly(paraphenyleneethynylene) (PPE) fluorescent conjugated polymer was assembled on either a quartz substrate (system I) or on the surface of silver nanocube (AgNC) monolayers (system II). The fluorescence intensity of the polymer was studied in system I as a function of the surface density of the polymer sample when deposited on quartz substrates and in system II on the surface coverage of the underlying AgNC monolayers. In system I, a continual increase in the fluorescence intensity is observed as the surface density of excited polymer is increased. In system II, the fluorescence intensity of the polymer first increased until a threshold surface coverage of AgNC was reached, after which it decreased rapidly with increasing surface coverage in the AgNC monolayer. The exciting light intensity dependence is studied before and after this threshold in system II. The results suggest that one-photon processes were responsible for the increased intensity before the threshold, and two-photon processes were responsible for the rapid decrease in the polymer fluorescence intensity after the threshold. These observations are explained by the increase of the surface plasmon enhancement of the exciting light intensity as the nanoparticle surface coverage is increased. In turn, this increases the polymer absorption rate, which results in a continuous increase in the exciton density and is evident by an increase in the fluorescence intensity. At the threshold, the increased exciton density leads to an increase in the rate of exciton-exciton collisions, which leads to exciton-exciton annihilations. When this phenomenon becomes faster than the rate of fluorescence emission, an intensity decrease is observed. By exploiting the surface plasmon enhancement of absorption processes, we have observed the first exciton-exciton annihilation using a low-intensity Hg-lamp continuous wave source.

The synthesis of two novel, water-soluble, sugar-substituted poly(p-phenyleneethynylene)s and their interactions with concanavalin A (Con A) and bacteria (Escherichia coli) are reported, and the issue of sensitivity enhancement is investigated. Both sugar-substituted PPEs (P5 and P7) exhibited strong interactions with Con A with K SV values exceeding 108 M−1. The binding constants between the sugar-substituted polymers and Con A were also quantitatively calculated using isothermal titration calorimetry (ITC) resulting in association constants as high as 106 M−1. P5 and P7 strongly interact with mannose-binding E. coli, which led to their aggregation.