핵산 폴리아닐린 계 센서

Summary

Nucleic acids are common analytes for assessing biological systems; however, bias from enzymatic manipulation can cause concern. Here a method is described for label-free detection of nucleic acids using polyaniline. This sensitive, cost-effective sensor technology can distinguish single nucleotide differences between molecules.

Abstract

Detection of nucleic acids is at the center of diagnostic technologies used in research and the clinic. Standard approaches used in these technologies rely on enzymatic modification that can introduce bias and artifacts. A critical element of next generation detection platforms will be direct molecular sensing, thereby avoiding a need for amplification or labels. Advanced nanomaterials may provide the suitable chemical modalities to realize label-free sensors. Conjugated polymers are ideal for biological sensing, possessing properties compatible with biomolecules and exhibit high sensitivity to localized environmental changes. In this article, a method is presented for detecting nucleic acids using the electroconductive polymer polyaniline. Simple DNA “probe” oligonucleotides complementary to target nucleic acids are attached electrostatically to the polymer, creating a sensor system that can differentiate single nucleotide differences in target molecules. Outside the specific and unbiased nature of this technology, it is highly cost effective.

Introduction

Conjugated polymers provide many options for molecular sensors. This includes fluorescence, electronic, and colorimetric responses¹. There have been many efforts to incorporate conjugated polymers in nucleic acid sensors. However, most systems require secondary detection, limiting sensing options². Recently, we reported a conjugated polymer-based sensor platform built on polyaniline (PANI) that exploits properties of this polymer, creating a label-free system³. PANI is an extensively conjugated electro-active polymer with properties such as fluorescence and resistance that are suitable for measuring biological systems⁴. The excitons within the structure are not localized leading to mobility of the positive charge between monomeric subunits. This provides a flexible scaffold of positive charges that can interact with the negatively charged backbone of DNA^5,6. Importantly, electrostatically attached DNA is orientated such that nitrogenous bases can participate in base pairing. Association with DNA alters the electronic properties of PANI, an effect that can be enhanced by UV irradiation (Figure 1)³. Using this system, oligonucleotides complementary to target nucleic acids can be immobilized on PANI. Multiple studies have demonstrated that upon hybridization electrostatically adsorbed oligonucleotides dissociate from PANI or other cationic matrices due to conformational changes caused by the switch to a double-stranded DNA structure^3,5,7.

In a sensor system where probe attachment modulates conjugated polymer properties, hybridization events can be transduced without labels or enzymatic modification of probes or target nucleic acids. Conjugated polymers offer great flexibility in detection methods, one of which is fluorescence. Through monitoring PANI fluorescence, concentrations of target nucleic acids as low as 10^-11 M (10 pM) can be detected³. Detection is rapid, occurring within 15 minutes of hybridization, and specific where a single mismatch in a target molecule can be differentiated³.

Fabrication of PANI-sensors is straightforward. High molecular weight PANI can be generated that is well-dispersed in water using standard synthesis procedures involving aniline monomer, surfactant, and controlled addition of an oxidant. Yield can be very high and unreacted oxidant removed by washing with water, ensuring no further PANI growth. PANI-probe association occurs spontaneously upon mixture, and complex formation is enhanced by mild UV exposure. Hybridization can be carried out immediately, and the changes in PANI fluorescence assayed following a short incubation. The simplicity of this technology makes it highly accessible to many laboratories.

Protocol

1. 처리 가능한 PANI 합성 250 mL 둥근 바닥 플라스크에 클로로 폼 60㎖를 완전히 (1 ㎖, 11 밀리몰) 아닐린을 녹인다. 600 5 분 동안 회전과 얼음 0-5 ° C까지 시원한에서 저어. 이것은 일반적으로 15 ~ 20 분 (그림 2A)를합니다. 600 rpm으로 교반하면서 둥근 바닥 플라스크 내의 아닐린 용액에 소듐 도데 실 벤젠 설포 네이트 (NaDBS) (7.44 g, 21 밀리몰)을 추가한다. 20 ml의 물에 황…

Representative Results

도 2a는 APS 부가 전 중합 공정, 즉 개시시 반응 셋업을 캡처한다. 미셀 형성은 미셀 계면 프로세스 PANI 합성이 발생하는 반응의 초기 단계이다.도 2b는 5 분 후에 유백색 용액을 나타낸다. APS 반응 첨가 후 30 분 약간 갈색으로 변.도 2c는 올리고머의 형성과 연관된 색상 변화를 보여준다.도 2D가 함께 일관성 단쇄 PANI의 …

Discussion

핵산의 PANI 기반 센서는 DNA 및 RNA와 상호 작용하기 위해서 물에 대한 중합체의 용해를 필요로한다. 물 PANI의 분산 이전 ^8보고 미셀을 형성하는 계면 활성제를 사용하여 달성된다. 4- sulfophthalic 산 도데 실 에스테르와 같은 다른 음이온 성 계면 활성제 여기서 사용 NaDBS 이외에도, 노닐 페놀에 톡실 레이트, 또는 세틸 트리메틸 암모늄 브로마이드와 같은 양이온 성 계면 활성제 등의 비이 온성…

Materials

Aniline	Fisher Scientific	A7401-500	ACS, liquid, refrigerated
Ammonium peroxydisulfate	Fisher Scientific	A682-500	ACS, crystalline
Sodium dodecylbenzene sulfonate	Pfaltz & Bauer	D56340	95% solid
Chloroform	Fisher Scientific	MCX 10601	Liquid
DNA primers	MWG operon	n/a	custom DNA sequence ~20bps
Microplate	USA Scientific	1402-9800	96 well, polypropylene as it is unreactive to chloroform
Microplate Adhesive Film	USA Scientific	2920-0000	Reduces well-to-well contamination, sample spillage and evaporation
Microscope Cover Glass	Fisher Scientific	12-544-D	PANI coated on UV irradiated cover glass
UV crosslinker	UVP	HL-2000	Energy: X100 μJ/cm2; Time: 2min
Hybridization Oven	VWR	01014705 T	Temperature: 400C; with rocking for 15 min
Glass Apparatus	Fisher Scientific		Three necked round bottom flask for reaction; dropping funnel, stoppers, condenser, separating funnel
Microscope	Leica Microsystems	Leica IMC S80	Magnification 20X; Pseudo color 536 nm; Exposure 86 ms; Gain 1.0X; Gamma 1.6
Microplate Reader	Molecular Devices	89429-536