We report here for the first time on the use of potentiometry for ultrasensitive nanoparticlebased detection of protein interactions. In particular, a silver ion-selective electrode (ISE) is used as an effective transducer for sandwich immunoassays in connection to the capture and silver enlargement of gold nanoparticle tracers. It is anticipated that this approach may form the basis for highly sensitive bioaffinity assays.Nanoparticle-based electrochemical detection of proteins has recently received considerable attention. These include the use of gold 1 and semiconductor 2 nanocrystal tracers, as well as carbon-nanotube-derived amplification of the recognition and transduction events 3 and colloidal gold labels with carbon paste electrode substrates. 4 These nanoparticle-based electrochemical immunoassays commonly rely on anodic stripping voltammetry (ASV) due to its intrinsic preconcentration step that allows one to achieve ultratrace level detection limits. 5Recent improvements in the detection limits of ion-selective electrodes based on polymeric membranes containing selective receptors (ionophores) yielded sensors for the direct measurement in the subnanomolar concentration range. 6 This was made possible by minimizing passive zero current ion fluxes from the membrane into the sample solution. 7,8 Recent approaches include the development of trace level potentiometric sensing membranes backside contacted with conducting polymers as ion-to-electron transducers, 9 monolithic columns as membrane supports, 10 and polymeric membranes with optimized aqueous inner solutions. 6 It is now possible to use miniaturized ISEs for detecting femtomole amounts of ions in microvolume samples 11,12 since there is no expected deterioration of the signal or detection limit as the sample volume is reduced. We show here that such microsensors may be very attractive systems for the ultrasensitive detection of bioassays when coupled to nanoparticle amplification labels.Scheme 1 outlines the new particle-based biosensing protocol. It is based on a sandwich immunoassay where the target mouse IgG antigen is captured by the primary anti-mouse IgG antibody modified gold substrate, followed by adding a secondary anti-mouse IgG antibody conjugated to gold nanoparticle tags and by catalytic silver enlargement onto the gold labels. The precipitated silver is oxidatively dissolved with hydrogen peroxide to yield dilute pretsche@ethz.ch; joseph.wang@asu.edu; bakkere@purdue.edu. † Purdue University. ‡ ETH Zürich. § Arizona State University. Supporting Information Available:Experimental details, instrumentation, reagents, and construction of the silver ion-selective microelectrode. This material is available free of charge via the Internet at http://pubs.acs.org. To amplify the mouse IgG signal, silver enhancement was used after the immunoassay. Such enhancement aims at catalytic deposition of silver on the gold tags, while avoiding spontaneous deposition onto other components of the assay. Because analogous optical methods rely on a threshol...

Cuproptosis, a newly identified form of regulated cell death that is copper‐dependent, offers great opportunities for exploring the use of copper‐based nanomaterials inducing cuproptosis for cancer treatment. Here, a glucose oxidase (GOx)‐engineered nonporous copper(I) 1,2,4‐triazolate ([Cu(tz)]) coordination polymer (CP) nanoplatform, denoted as GOx@[Cu(tz)], for starvation‐augmented cuproptosis and photodynamic synergistic therapy is developed. Importantly, the catalytic activity of GOx is shielded in the nonporous scaffold but can be “turned on” for efficient glucose depletion only upon glutathione (GSH) stimulation in cancer cells, thereby proceeding cancer starvation therapy. The depletion of glucose and GSH sensitizes cancer cells to the GOx@[Cu(tz)]‐mediated cuproptosis, producing aggregation of lipoylated mitochondrial proteins, the target of copper‐induced toxicity. The increased intracellular hydrogen peroxide (H2O2) levels, due to the oxidation of glucose, activates the type I photodynamic therapy (PDT) efficacy of GOx@[Cu(tz)]. The in vivo experimental results indicate that GOx@[Cu(tz)] produces negligible systemic toxicity and inhibits tumor growth by 92.4% in athymic mice bearing 5637 bladder tumors. This is thought to be the first report of a cupreous nanomaterial capable of inducing cuproptosis and cuproptosis‐based synergistic therapy in bladder cancer, which should invigorate studies pursuing rational design of efficacious cancer therapy strategies based on cuproptosis.

Here we present the first report on nanoparticle-based biosensing of glycan markers of diseases. The protocol relies on the competition between a nanocrystal (CdS)-tagged sugar and the target sugar for the binding sites of surface-confined lectin and monitoring the extent of competition through highly sensitive electrochemical detection of the captured nanocrystal. This development is expected to allow decentralized detection of carbohydrate moieties and lectin-carbohydrate interactions to be performed more rapidly, sensitively, inexpensively, and reliably.

Self-assembled monolayers (SAMs) of thioglycolic acid, 3-mercaptopropionic acid, 11-mercaptoundecanoic acid, 16-mercaptohexadecanoic acid and bis(carboxydecyl) disulÐde are formed on gold electrodes, respectively. The surface of the x-terminal acid groups in these monolayers are determined using pK a s electrochemical titration, to be 6.1, 5.3, 7.3, 7.9 and 7.3, respectively. The e †ect of chain length on the surface values of x-carboxy alkanethiol SAMs is described. The SAM has a strong inÑuence on the heterogeneous pK a electron transfer rate constant, of the electroactive probe The values of k s , Fe(CN) 6 3~. k s Fe(CN) 6 3~, determined with cyclic voltammetry at the pH values of the inÑection point of the electrochemical titration curves for the four monolayers with carbon number 2, 3, 11 and 16, are calculated to be 7.4 ] 10~3, 4.6 ] 10~3, 4.4 ] 10~3 and 2.6 ] 10~3 cm s~1, respectively. The e †ect of time of immersion for monolayer formation on the defects present in the SAMs formed is discussed. The SAMs of bis(carboxydecyl) disulÐde and 11-mercaptoundecanoic acid show the same surface and values and thus possess the same surface pK a k s properties.

A novel strategy for immunoassay and the preparation of reagentless immunosensors was proposed. This strategy was based on the immobilization of antigen and the direct electrochemistry of horseradish peroxidase (HRP) that was labeled to an antibody. A reagentless immunosensor for carcinoma antigen-125 (CA 125) determination was developed. The immunosensor was prepared by immobilizing CA 125 with titania sol-gel on a glassy carbon electrode by the vapor deposition method. The incubation of the immunosensor in phosphate buffer solution (PBS) including HRP-labeled CA 125 antibody led to the formation of a HRP-modified surface. The immobilized HRP displayed its direct electrochemistry with a rate constant of 3.04 +/- 1.21 s(-1). With a competition mechanism, a differential pulse voltammetric determination method for CA 125 was established by the peak current decrease of the immobilized HRP. The current decrease resulted from the competitive binding of the CA 125 in sample solution and the immobilized CA 125 to the limited amount of HRP-labeled CA 125 antibody. Under optimal conditions, the current decrease was proportional to CA 125 concentration ranging from 2 to 14 units mL(-1) with a detection limit of 1.29 units mL(-1) at a current decrease by 10%. The CA 125 immunosensor showed good accuracy and acceptable precision and fabrication reproducibility with intraassay CVs of 8.7 and 5.5% at 8 and 14 units mL(-1) CA 125 concentrations, respectively, and interassay CV of 19.8% at 8 units mL(-1). The storage stability was acceptable in a pH 7.0 PBS at 4 degrees C for 15 days. The proposed method provided a new promising platform for clinical immunoassay.