STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on May 25, 2017, is named 112624_00851_SL.txt and is 217,680 bytes in size.

BACKGROUND

Synthetic biology is an emerging discipline that has great potential to respond to global pandemics. The increasing ability of synthetic biologists to repurpose and engineer natural biological components for practical applications has led to new opportunities for molecular diagnostics.

In the case of viral outbreaks, standard serological approaches such as antibody detection have limited diagnostic value due to cross-reactivity in patients that have previously been infected by other flaviviruses circulating in the region. As a result, accurate diagnosis requires nucleic acid-based detection methods, such as PCR and isothermal nucleic acid amplification. However, such techniques are expensive, require technical expertise to run and interpret, and use equipment that is incompatible with use in remote and low-resource locations where surveillance and containment are critically needed. Accordingly, there remains a need in the art for improved methods and devices for rapid detection of target nucleic acids, including pathogen-specific nucleic acids for infection detection and for accurate strain identification.

BRIEF SUMMARY

In a first aspect, provided herein is a method of detecting a target nucleic acid in a sample. In some cases, the method comprises or consists essentially of the steps of: (a) obtaining nucleic acid from a biological sample obtained from a subject; (b) amplifying the nucleic acid using isothermal amplification; (c) contacting the amplified nucleic acid to a toehold switch, wherein the toehold switch encodes a reporter protein and comprises one or more single-stranded toehold sequence domains that are complementary to a target nucleic acid or the reverse complement thereof, wherein the contacting occurs under conditions that allow translation of the coding domain in the presence of the target nucleic acid but not in the absence of the target nucleic acid, and detecting the reporter protein as an indicator that the target nucleic acid is present in the amplified nucleic acid of the subject; and (d) identifying the target nucleic acid as containing a target protospacer adjacent motif (PAM), wherein identifying comprises: (i) amplifying nucleic acid obtained from the biological sample using a reverse primer designed to append the trigger sequence of one or more toehold switch sequence domains; (ii) contacting the amplified nucleic acid of (i) to CRISPR/Cas under conditions that allow for sequence-specific cleavage of the contacted nucleic acid by CRISPR/Cas when the target PAM is present in the amplified nucleic acid; and (iii) detecting activation of the toehold switch, wherein activation does not occur in the event of CRISPR/Cas-mediated sequence-specific cleavage, thereby indicating the presence of the target PAM. The toehold switch can comprise one or more single-stranded toehold sequence domains, a fully or partially double-stranded stem domain comprising an initiation codon, a loop domain comprising a ribosome binding site, and a coding domain. The toehold and stem domains can be complementary in sequence to a naturally occurring RNA. The loop domain can be complementary in sequence to a non-naturally occurring RNA. The target nucleic acid can be an RNA specific to a pathogen. The pathogen is selected from the group consisting of a virus, bacterium, fungus, and parasite. In some cases, the pathogen is a virus. The virus can be Zika virus. The virus can an American Zika variant (GenBank: KU312312). The virus strain can be an African Zika variant (GenBank: KF268950). The toehold switch can comprise anE. colilacZ gene encoding β-galactosidase. Detecting activation of the one or more toehold switch sensors can comprise performing a LacZ-based colorimetric assay. Isothermal amplification can be selected from the group consisting of NASBA (nucleic acid sequence-based amplification), loop-mediated isothermal amplification (LAMP), recombinase polymerase amplification (RPA), and helicase-dependent amplification (HDA). The biological sample can be selected from the group consisting of blood, serum, urine, saliva, tissue, cell, and organ, or a fraction or portion thereof.

In another aspect, provided herein is a method of detecting a target nucleic acid in a sample. In some cases, the method comprises or consists essentially of: (a) obtaining RNA from a biological sample obtained from a subject; (b) amplifying the RNA using isothermal amplification; (c) contacting the amplified RNA to a toehold switch, wherein the toehold switch encodes a reporter protein and comprises one or more single-stranded toehold sequence domains that are complementary to a target RNA or the reverse complement thereof, wherein the contacting occurs under conditions that allow translation of the coding domain in the presence of the target RNA but not in the absence of the target RNA, and detecting the reporter protein as an indicator that the target RNA is present in the amplified RNA of the subject; and (d) identifying the target RNA as containing a target protospacer adjacent motif (PAM), wherein identifying comprises: (i) amplifying RNA obtained from the biological sample using a reverse primer designed to append the trigger sequence of one or more toehold switch sequence domains; (ii) contacting the amplified RNA of (i) to CRISPR/Cas under conditions that allow for sequence-specific cleavage of the contacted RNA by CRISPR/Cas when the target PAM is present in the amplified RNA; and (iii) detecting activation of the toehold switch, wherein activation does not occur in the event of CRISPR/Cas-mediated sequence-specific cleavage, thereby indicating the presence of the target nucleic acid. The toehold switch can comprise one or more single-stranded toehold sequence domains, a fully or partially double-stranded stem domain comprising an initiation codon, a loop domain comprising a ribosome binding site, and a coding domain. The toehold and stem domains can be complementary in sequence to a naturally occurring RNA. The loop domain can be complementary in sequence to a non-naturally occurring RNA. The target nucleic acid can be an RNA specific to a pathogen. The pathogen can be selected from the group consisting of a virus, bacterium, fungus, and parasite. In some cases, the pathogen is a virus. The virus can be Zika virus. The virus can be an American Zika variant (GenBank: KU312312). The virus can be an African Zika variant (GenBank: KF268950). The toehold switch can comprise anE. colilacZ gene encoding β-galactosidase. Detecting activation of the one or more toehold switch sensors can comprise performing a LacZ-based colorimetric assay. Isothermal amplification can be selected from the group consisting of NASBA (nucleic acid sequence-based amplification), loop-mediated isothermal amplification (LAMP), recombinase polymerase amplification (RPA), and helicase-dependent amplification (HDA). The biological sample is selected from the group consisting of blood, serum, urine, saliva, tissue, cell, and organ, or a fraction or portion thereof.

In a further aspect, provided herein is a method of detecting presence of virus in a sample. The method can comprise or consist essentially of the steps of: (a) obtaining RNA from a biological sample obtained from a subject; (b) amplifying the RNA using isothermal amplification; (c) contacting the amplified RNA to a toehold switch, wherein the toehold switch encodes a reporter protein and comprises one or more single-stranded toehold sequence domains that are complementary to an endogenous virus RNA sequence or the reverse complement thereof, wherein the contacting occurs under conditions that allow translation of the coding domain in the presence of the endogenous virus RNA but not in the absence of the endogenous virus RNA, and detecting the reporter protein as an indicator that the endogenous virus RNA is present in the amplified RNA of the subject. The virus can be Zika virus. The toehold switch can comprise one or more Zika genome-specific single-stranded toehold sequence domains, a thermodynamically stable double-stranded stem domain, a loop domain comprising a ribosome binding site, and a coding domain. The loop domain can be complementary in sequence to a naturally occurring RNA. The loop domain can be complementary in sequence to a non-naturally occurring RNA. The loop domain can be 11 nucleotides or 12 nucleotides. The toehold switch can comprise anE. colilacZ gene encoding β-galactosidase. Isothermal amplification can be selected from the group consisting of NASBA (nucleic acid sequence-based amplification), loop-mediated isothermal amplification (LAMP), recombinase polymerase amplification (RPA), and helicase-dependent amplification (HDA).

In another aspect, provided herein is a device for identifying a pathogen, comprising a preserved paper test article, wherein a methods described herein is performed using the preserved paper test article. The paper test article can be preserved by freeze-drying.

In another aspect, provided herein is a kit for detecting a pathogen, comprising one or more of a device as described herein and an electronic optical reader.

In a further aspect, provided herein is a method of genotyping a nucleic acid molecule. The method can comprise or consist essentially of contacting the nucleic acid molecule with: a programmable nuclease; and a sgRNA, wherein the combination of the nuclease and sgRNA can specifically bind to at least one sequence variant of the nucleic acid molecule; and detecting the presence or absence of a cut in the nucleic acid molecule generated by the nuclease. In some cases, the method further comprises a first step of performing reverse transcription on a RNA molecule and performing 2nd strand DNA synthesis with a toehold primer to generate the nucleic acid molecule; and wherein the detecting step comprises: transcribing an RNA from the nucleic acid molecule after contacting it with the nuclease, using a primer which initiates transcription from a location distal of the sequence variation site with respect to the location of the toehold primer sequence; and contacting a sensor with the RNA resulting from step a) and detecting the presence or absence of sensor activation; wherein the sensor is activated if the nuclease is not able to cut the nucleic acid molecule in step a). The presence of a cut can indicate that the nucleic acid molecule has a sequence variant to which the sgRNA and nuclease can specifically bind. The presence of a cut can indicate that the nucleic acid molecule has a sequence variant to which the nuclease specifically binds. The programmable nuclease can be Cas. The sequence variant can occur at a PAM site. The nucleic acid molecule can be of human, animal, prokaryotic, eukaryotic, pathogenic, or synthetic origin. The nucleic acid molecule can be of viral origin. The viral nucleic acid molecule can be a Zika virus nucleic acid molecule. The sequence variant being detected can differentiate at least one of the African, American, and Asian Zika strains from the others. The sequence variant can be selected from Table 2. The sequence variant being detected can differentiate the African and American Zika virus strains. The sequence variant can be the SNP occurring at site 7330 of the African (GenBank: KF268950) and American (GenBank: KU312312) Zika strains. The sgRNA can have the sequence of SEQ ID NO: 1.

In another aspect, provided herein is a composition comprising a sgRNA which can specifically bind to a sequence flanking at least one sequence variant selected from Table 2, wherein the sequence variation occurs at a CRISPR/Cas PAM binding site. The sgRNA can comprise SEQ ID NO: 1. The sgRNA can be selected from Table 2.

In a further aspect, provided herein is a composition comprising a CRISPR/Cas nuclease and a sgRNA that specifically binds to a sequence flanking at least one sequence variant occurring in a population. The population can be a viral population. The viral population can be a Zika virus population. The variant can be selected from Table 2. The sgRNA can be selected from Table 2. The sgRNA can comprise SEQ ID NO: 1.

These and other features, objects, and advantages of the present invention will become better understood from the description that follows. In the description, reference is made to the accompanying drawings, which form a part hereof and in which there is shown by way of illustration, not limitation, embodiments of the invention. The description of preferred embodiments is not intended to limit the invention to cover all modifications, equivalents and alternatives. Reference should therefore be made to the claims recited herein for interpreting the scope of the invention.

