Acquiring multiple signals along with the reaction time: improving recognition capability of a multidimensional colorimetric sensor array for sensitive protein detection.

The development of sensitive and cheap sensor arrays for identification of proteins plays an important role in many bioanalytical and clinical investigations. Here, we introduce a multidimensional colorimetric sensor array for the detection of multiple proteins based on acquiring multiple signals along with the reaction time to enhance the discrimination ability. In a single experiment, the unique fingerprint for each protein against the sensor array is generated from a response absorbance signal at three reaction time points (at 10 min, 15 min, and 20 min). Our colorimetric sensing system is able to identify ten proteins not only in aqueous solution at 10 nM but also in human urine at the 50 nM level with an accuracy of 100%. Moreover, the identification of HSA in urine at the nanomolar level within a linear range of 0.05-1.0 µM is achieved. Our sensing array system is sufficiently sensitive for the discrimination of pure HSA, binary mixtures of HSA and Lys at a total concentration of 50 nM in urine. This study indicates that the application of the real-time resolved response signals enables the enhancement of the discrimination ability for protein recognition.

Ratiometric fluorescence sensor arrays based on quantum dots for detection of proteins.

Optical cross-reactive sensor arrays have recently been demonstrated as a powerful tool for high-throughput protein analysis. Nevertheless, applying this technology to protein detection is complicated by many external factors, such as the interfering substances, the background noise, and sample environmental changes in the biological matrix. Herein we demonstrate that a ratiometric fluorescence sensor array based on quantum dots can be employed to circumvent these limitations. Several intrinsic dual-emitting Mn-doped quantum dots capped with different organic functional groups were designed as sensing elements. Distinct and reproducible response patterns against the ratiometric sensor array were obtained from ten proteins in a buffer of different pH (pH 5.7, 7.4, and 8.3) and spiked into human urine. Linear discrimination analysis of the response patterns showed successful differentiation of the analytes at concentrations as low as 50 nM with high identification accuracy. Furthermore, this sensor system also enables the detection of these eight proteins (at 500 nM) in human urine without any treatment. The ratiometric fluorescence change from quantum dots for analysis of proteins can eliminate effectively the signal interference from the pH value change and the fluorescent background in human urine. The present study will open a new avenue to improve the discrimination ability of sensor arrays.

A nanoplasmonic probe as a triple channel colorimetric sensor array for protein discrimination.

The salt-induced aggregation, nanoparticle regrowth and self-assembly behaviors of gold nanoparticles (AuNPs) and DNA conjugates could be changed after interaction with different proteins, generating various color changes and a unique fingerprint pattern for each protein. The triple-channel colorimetric signals have been employed for protein discrimination with the naked eye.

Multidimensional sensor for pattern recognition of proteins based on DNA-gold nanoparticles conjugates.

We presented an extensible multidimensional sensor with conjugated nonspecific dye-labeled DNA sequences absorbed onto gold nanoparticles (DNA-AuNPs) as receptors. At the presence of target protein, DNA was removed from the surface of AuNPs due to the competitive binding, which resulted in a red-to-blue color change along with salt-induced aggregation of AuNPs for colorimetric analysis and fluorescent "turn-on" signal of the labeled dye for fluorescence analysis. The orthogonal and complementary fluorescent and colorimetric signals obtained from each protein were applied to distinguish different proteins. By simply changing the DNA sequences, more dual-channel sensing elements could be easily obtained and added into this multidimensional sensor. This enhanced its discriminating power to the proteins. With three sensing elements, our extensible multidimensional sensing platform exhibited excellent discrimination ability. Eleven proteins at the concentration of 50 nM had been classified with accuracies of 100% by using linear discriminant analysis (LDA). Remarkably, two similar proteins [bovine serum albumin (BSA) and human serum albumin (HSA)] at various concentrations and the mixture of these two proteins with different molar ratios had been successfully discriminated in one LDA plot as well. Furthermore, in the presence of human urine sample, 10 proteins at 1.0 µM could also be well-discriminated. The accuracy of discrimination of unknown samples was all 100% for these experiments. This strategy is a complement of the multidimensional sensing system and traditional sensor platform, offering a new way to develop sensitive array sensing systems.

Continuously evolving 'chemical tongue' biosensor for detecting proteins.

We developed a unique continuously evolving colorimetric sensor array based on AuNPs decorated by two single-stranded oligonucleotides with different molar ratios for protein discrimination. The number of differential receptors in this sensor array could be easily extended by adjusting the molar ratios of two DNA, resulting in continuously improved discrimination ability. The continuous response data of target samples against our sensing system could be easily obtained and exclude abnormal signals. The sensing system could discriminate twelve proteins at the concentration of 200nM in the presence of 50% human urine with accuracy of 100%, showing feasible potential for diagnostic applications. Remarkably, HSA at various concentrations, the pure Lys and HSA, and the mixture of these two proteins with different molar ratios had been successfully discriminated in LDA plot as well in the presence of human urine sample. This novel strategy will be very promising for the design of cheaper and more reliable sensor arrays for target samples.

Multidimensional colorimetric sensor array for discrimination of proteins.

An extensible multidimensional colorimetric sensor array for the detection of protein is developed based on DNA functionalized gold nanoparticles (DNA-AuNPs) as receptors. In the presence of different proteins, the aggregation behavior of DNA-AuNPs was regulated by the high concentrations of salt and caused different color change; while DNA-AuNPs grew induced by the reduction of HAuCl4 and NH2OH as a reductant on the surface of nanoparticles exhibited different morphologies and color appearance for different proteins. The transducers based on AuNPs modified by specific and nonspecific DNA enables naked-eye discrimination of the target analytes. This extensible sensing platform with only two receptors could simultaneously discriminate ten native proteins and their thermally denatured conformations using hierarchical cluster analysis (HCA) at the concentration of 50nM with 100% accuracy. This opens up the possibility of the sensor array to investigate the different conformational changes of biomacromolecules, and it gives a new direction of developing multidimensional transduction principles based on plasmonic nanoparticle conjugates. Furthermore, the sensing system could discriminate proteins at the concentration of 500nM in the presence of 50% human urine, which indicated this sensor array has great potential ability in analyzing real biological fluids. In addition, the multidimensional colorimetric sensor array is suitable for analysis of target analytes in the resource-restricted regions because of rapid, simple, low cost, and in-field detection with the naked eye.